LH gratefully acknowledges financial support by an US National Science Foundation Graduate Research Fellowship under Grant No. 1148897. Electron microscopy characterization and SPS processing at UC Davis was financially supported by a University of California Laboratory Fee award (#12-LR-238313). Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

1. Sample Preparation of Single Crystal Strontium Titanate
NOTE: Single crystal STO is supplied with a (100) surface polished to a mirror finish.
<ol>
	<li>Section STO into 5x5 mm2 pieces using diamond wire saw.</li>
	<li>Ultrasonically clean samples at 50-60 Hz consecutively in baths of acetone, isopropanol, and methanol for fifteen minutes each.</li>
	<li>Remove STO from methanol bath to immediately place on hot plate held at a temperature of 200 &#176;C. Heating the sample after cleaning prevents formation of evaporation spotting from the alcohol.</li>
	<li>Place samples for ten minutes in buffered hydrofluoric acid (pH=4), a 6:1 solution of ammonium fluoride and 49% hydrofluoric acid.22 This solution etches the STO, forming a predominantly (100) TiO2 terminated surface. If the optically flat side of the single crystal has a rainbow patina, the sample has been over-etched and should not be used.</li>
	<li>After ten minutes in the etchant solution, rinse samples in deionized (DI) water and then in isopropanol. Dry using clean house air.</li>
</ol>
2. Bicrystal Formation via Spark Plasma Sintering Apparatus
NOTE: For 5x5 mm2 crystal use a 30 mm diameter graphite die. If a die with a diameter smaller than 30 mm is used, the bicrystal catastrophically fractures during bonding. Optimal die size as well as pressure exerted by the SPS apparatus is highly dependent on the size of the crystals.
<ol>
	<li>Place a 30 mm circle of graphite paper on a graphite plunger with a 30 mm diameter. Graphite paper prevents STO from bonding to the graphite plunger during the experiment.</li>
	<li>Stack two 5x5 mm2 STO single crystals with their optically flat surfaces placed facing inward to form the bicrystal boundary. Center the stack on top of the graphite paper and plunger.</li>
	<li>Rotate the top single crystal around the &#60;100&#62; axis to a chosen misorientation angle. The &#60;100&#62; axis is perpendicular to the optically flat surface of crystal.</li>
	<li>Slide the graphite die over the plunger and crystals. Place a second 30 mm diameter circle of graphite paper and then 30 mm diameter plunger over the stacked STO crystals.</li>
	<li>Stack the combined plungers and die onto the graphite spacers in SPS apparatus (Figure 1).</li>
	<li>Apply a uniaxial force of 3 kN to minimize contact resistance using the z-axis control buttons. Throughout the experiment, the user must keep the force at 3 kN via the z-axis control buttons.</li>
	<li>Insert k-type thermocouple into graphite die at the small hole, shown in Figure 1. The thermocouple extends through the die to the sample.</li>
	<li>Set the chamber pressure of the SPS apparatus to ~10 Pa using the vacuum push buttons.</li>
	<li>Select bond temperature, time, and heating rates via program instrument control software (Table 1). For the bonding temperature and time, use a heating rate of 70-80 &#176;C/min and a cooling rate of 50 &#176;C/min.</li>
	<li>Set 12 s on, 2 s off DC pulse using the instrument sintering button. A pulsed bias of ~ 4 V and direct current of ~550 A are applied incrementally to the sample once the program is set to run.</li>
	<li>Press the start button on the machine.</li>
	<li>Remove the sample when the program ends. After bicrystal formation, the sample will appear grey-black due to the reducing environment of the SPS apparatus.</li>
	<li>Use a high temperature furnace at a temperature of 1,200 &#176;C for 140 h, apply no pressure during this procedure, to anneal and re-oxidize the sample in air. Annealing parameters were selected according to previous work done by Hutt et al. in which bicrystals formed in high vacuum13. After annealing, the sample reveals an off-white color and is oxidized.</li>
</ol>
3. Sample Preparation of Bicrystal for Electron Beam Imaging
<ol>
	<li>Cross-section bicrystal with diamond wire saw into 5x1 mm2 sections.</li>
	<li>Polish cross-section samples with diamond lapping film. The grit size on the diamond lapping film is gradually decreased from 9 &#181;m to 0.1 &#181;m. Change to smaller grit size once scratches are uniform across the surface. Use a counter clockwise platen motion for 9 &#181;m to 6 &#181;m lapping film. Use a counter clockwise platen motion with an oscillating sample head for 6 &#181;m to 0.1 &#181;m lapping film.</li>
	<li>Polish cross-section samples with colloidal silica for two minutes using a mat cloth. Continuously pour colloidal silica onto the mat with counter clockwise platen motion and oscillating sample head.</li>
	<li>Fifteen seconds before removing the sample, stop pouring colloidal silica and pour DI water onto platen. Pour DI water for fifteen seconds, remove sample, and immediately rinse sample in DI water for 1 min. If this procedure is not followed, the colloidal silica will bond the sample&#39;s surface and obscure the grain boundary during scanning electron microscopy (SEM).</li>
	<li>Once the sample is polished to an optically smooth surface, ultrasonically clean samples consecutively in baths of acetone, isopropanol, and methanol for fifteen minutes each.</li>
	<li>Remove STO from methanol bath to immediately place on hot plate held at a temperature of 200 &#176;C. Heating the sample after cleaning prevents formation of evaporation spotting from the alcohol.</li>
	<li>Mount sample polished surface up onto a sample stub using colloidal graphite.</li>
	<li>Sputter coat sample surface with 2-3 nm of carbon. Use the following parameters for the carbon coater: a pulse resolution of 0.2 nm/pulse, current step rate of 0.2 A/pulse, pulse current of 40 A, pulse length of 2 s, and maximum pulses of 50.</li>
</ol>
4. Cleaning the FIB Copper Grid
NOTE: Improper cleaning of the FIB grid can lead to carbon contamination of the lamella in the TEM.
<ol>
	<li>Place copper FIB grid in an acetone and then isopropanol bath for 1 h each.</li>
	<li>Plasma clean copper FIB grid for 10 min.</li>
</ol>
5. Preparation of Transmission Electron Microscopy (TEM) Lamella via Focused Ion Beam (FIB) Apparatus
NOTE: All parameters used in FIB preparation are typed or selected from a drop down menu in the FIB apparatus software.
<ol>
	<li>Place STO sample and copper FIB grid in FIB apparatus. The stage is at 7 mm.</li>
	<li>Find a region of interest along the interface between the two single crystals, i.e., the grain boundary.</li>
	<li>Select Patterning dialogue box. In Patterning Control, select the Rectangle Patterning Tool with application property C-e-dep surface. Insert C-dep for gas injection. Deposit a 15&#215;2&#215;2 &#181;m3 protective layer of carbon using the electron beam at a voltage of 5.0 kV, a current of 13.0 nA, and a tilt angle of 0&#176;. Retract C-dep.</li>
	<li>Select Patterning dialogue box. In Patterning Control, select the Rectangle Patterning Tool with application property W-dep. Insert W-dep for gas injection. Deposit 15&#215;2&#215;2 &#181;m3 protective layer of tungsten using the ion beam at a voltage of 30.0 kV, a current of 0.3 nA, and a tilt angle of 52&#176;. Retract W-dep.</li>
	<li>Select Patterning dialogue box. In Patterning Control, select the Regular Cross Section Patterning Tool with application property Si. Use 22&#215;25&#215;15 &#181;m3 for the bottom pattern and of 22&#215;27&#215;15 &#181;m3 for the top pattern at a voltage of 30.0 kV, a current of 30.0 nA, and a tilt angle of 52&#176; via the ion beam. The pattern will create a trench mill on both sides of the protective layer.</li>
	<li>Select Patterning dialogue box. In Patterning Control, select the Clean Cross Section Patterning Tool with application property Si. Use 22&#215;3&#215;60 &#181;m3 for the top and bottom pattern at a voltage of 30.0 kV and a current of 1.0 nA via the ion beam. The tilt angle is 53.5&#176; for the bottom pattern and 50.5&#176; for the top pattern. The pattern cleans the surface of the trenched lamella from the curtaining pattern that results from the regular cross section patterning.</li>
	<li>Cut a J-pattern into the sample using the Rectangle Patterning tool with application property Si. Use 2 &#181;m for the width at a voltage of 30.0 kV and a current of 1.0 nA via the ion beam.</li>
	<li>Select Easy Lift dialogue box. Insert the micromanipulator to the park position. Lower the micromanipulator and attach the sample to the copper FIB grid via a tungsten weld using the process detailed in 5.4.</li>
	<li>Using the steps detailed in 5.7, &#181;cut a U-pattern, continuing from the original J-pattern, in the sample using the ion beam at a voltage of 30.0 kV and a current of 1.0 nA.</li>
	<li>Lift the lamella via the micromanipulator above the bulk sample.</li>
	<li>Rotate the micromanipulator 180&#176;, so the grain boundary is no longer parallel to ion beam, but perpendicular to the ion beam.</li>
	<li>Tungsten weld the lamella to a copper FIB grid using the steps detailed in 5.4 with the ion beam at a voltage of 30.0 kV and a current of 0.3 nA.</li>
	<li>Cut the micromanipulator from the lamella using the steps detailed in 5.7 with the ion beam at a voltage of 30.0 kV and a current of 1.0 nA.</li>
	<li>Repeat the steps detailed in 5.3. Deposit a 15&#215;2&#215;4 &#181;m3 protective layer of carbon using an electron beam at a voltage of 5.0 kV, a current of 13.0 nA, and a tilt angle of 0&#176;.</li>
	<li>Repeat the steps detailed in 5.4. Deposit 15&#215;2&#215;8 &#181;m3 protective layer of tungsten using an ion beam at a voltage of 30.0 kV, a current of 0.3 nA, and a tilt angle of 52&#176;.</li>
	<li>With the ion beam, thin the sample to approximately 200 nm using a voltage of 30.0 kV and a systematically decreasing current of 0.5 nA, 0.3 nA, and 0.1 nA. At this stage, a cleaning cross section pattern is used and the sample is tilted to an angle of 52 &#177;&#177; 1.5&#176;.</li>
	<li>With the ion beam, thin the sample to electron transparency using a voltage of 5.0 kV and a current of 77.0 pA. At this stage, a rectangle pattern is used with a tilt angle of 52 &#177; 3&#176;.</li>
	<li>Remove amorphous damage incurred from the FIB by cleaning the sample at a voltage of 500 eV and a current of 150 &#181;A.</li>
	<li>Place TEM sample in TEM holder and insert holder in scanning transmission electron microscope (STEM). Select &#39;Capture&#39;, image sample grain boundary.</li>
</ol>

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We have nothing to disclose.

The bonding temperature of 1,200 &#176;C was chosen to maximize diffusion as small changes in temperature can greatly impact the kinetics of all diffusion bonding mechanisms. A temperature of 1,200 &#176;C is outside the brittle-ductile transition temperature range of STO. However, the sample underwent brittle fracture at this temperature. The catastrophic failure of the STO bicrystal was not unexpected as STO has ~ 0.5% ductility at 1,200 &#176;C. Also, the sample was held at a pressure of 140 MPa throughout the heating...

Spark plasma sintering (SPS) is a technique in which application of high uniaxial pressure and pulsed direct current leads to the rapid densification of powder compacts1. This technique also leads to the successful formation of composite structures from various materials, including silicon nitride/silicon carbide, zirconium boride/silicon carbide, or silicon carbide, with no additional sintering aids required2,3,4,5. The synthesis of these composite structures by conventional hot-pressing had been challenging in the past. While application of a high uniaxial pressure and fast heating rate via the SPS technique enhances consolidation of powders and composites, the phenomenon causing this enhanced densification debated in the literature2,3,6,7. There also exists only limited information regarding the influence of electric fields on grain boundary formation and the resulting atomic structures of grain boundary cores8,9. These core structures determine the functional properties of SPS sintered materials, including electric breakdown of high voltage capacitors and the mechanical strength and toughness of ceramic oxides10. Therefore, understanding the fundamental grain boundary structure as a function of SPS processing parameters, such as applied current, is necessary for the manipulation of a material&#39;s overall physical properties. One method to systematically elucidate the fundamental physical mechanisms underpinning SPS is the formation of specific grain boundary structures, i.e., bicrystals. A bicrystal is created by manipulation of two single crystals, which are then diffusion bonded with specific misorientation angles11. This method provides a controlled way to investigate the fundamental grain boundary core structures as a function of processing parameters, dopant concentration, and impurity segregation12,13,14.
Diffusion bonding is dependent on four parameters: temperature, time, pressure, and bonding atmosphere15. Conventional diffusion bonding of strontium titanate (SrTiO3, STO) bicrystals typically occurs at a pressure below 1 MPa, within a temperature range of 1,400-1,500 &#176;C, and time scales ranging from 3 to 20 hours13,14,16,17. In this study, bonding in a SPS apparatus is achieved at significantly lower temperature and time scales in comparison to conventional methods. For polycrystalline materials, reduced temperature and time scales via SPS significantly limits grain growth, thereby providing advantageous control of a material&#39;s properties through manipulation of its microstructure.
The SPS apparatus, for a 5&#215;5 mm2 sample, exerts a minimum pressure of 140 MPa. Within the conventional diffusion bonding temperature range, Hutt et al. report instantaneous fracture of STO when the bonding pressure exceeds 10 MPa18. However, STO exhibits temperature dependent plasticity behavior, indicating bonding pressure can exceed 10 MPa at specific temperatures. Above 1,200 &#176;C and below 700 &#176;C, STO exhibits some ductility, at which stresses greater than 120 MPa can be applied without instantaneous fracture of the sample. Within the intermediate temperature range of 700-1,200 &#176;C, STO is brittle and experiences instantaneous fracture at stresses greater than 10 MPa. At 800 &#176;C, STO has minor deformability prior to fracture at stresses less than 200 MPa19,20,21. Hence, bonding temperatures for STO bicrystal formation via SPS apparatus must be selected according to the plasticity behavior of the material.

<table><tbody><tr><td>Strontium titanate single crystal (100)</td><td>MTI Corporation</td><td>STOa101005S1-JP</td><td></td></tr><tr><td>Buffered oxide etch, hyrofluoric acid 6:1</td><td>JT Baker</td><td>&amp;nbsp;MBI 1178-03</td><td></td></tr><tr><td>Scanning electron microscope (SEM)</td><td>FEI</td><td>Model: 430 NanoSEM</td><td></td></tr><tr><td>SPS apparatus&amp;nbsp;</td><td>Sumitomo Coal Mining Co</td><td>Model: Dr. Sinter 5000 SPS Apparatus</td><td></td></tr><tr><td>High Temperature Furnace</td><td>Thermolyne</td><td>Model: 41600</td><td></td></tr><tr><td>Ultrasonic Cleaner</td><td>Bransonic</td><td>Model: 221</td><td></td></tr><tr><td>Mechanical polisher</td><td>Allied High Tech Products</td><td>15-2100-TEM</td><td></td></tr><tr><td>Diamond lapping film</td><td>3M</td><td>660XV</td><td>1 &amp;#956;m to 9 &amp;#956;m Grit Size</td></tr><tr><td>Diamond lapping film</td><td>3M</td><td>661X</td><td>0.5 &amp;#956;m to 0.1 &amp;#956;m Grit Size</td></tr><tr><td>Colloidal silica</td><td>Allied High Tech Products</td><td>180-20000</td><td>0.05 &amp;#956;m Grit Size</td></tr><tr><td>Sputter coater</td><td>QuorumTech</td><td>Model: Q150RES</td><td></td></tr><tr><td>Focused ion beam (FIB) instrument&amp;nbsp;</td><td>FEI</td><td>Model: Scios dual-beamed focused ion beam (FIB) instrument&amp;nbsp;</td><td></td></tr><tr><td>Nanomill TEM specimen preparation system</td><td>Fischione Instruments</td><td>Model: 1040</td><td></td></tr><tr><td>Transmission electron microscope (TEM)&amp;nbsp;</td><td>JEOL</td><td>Model: JEM2500 SE&amp;nbsp;</td><td></td></tr><tr><td>Scanning transmission electron microscope (STEM)</td><td>FEI</td><td>Model: TEAM 0.5&amp;nbsp;</td><td></td></tr></tbody></table>

spark plasma sintering apparatus used for the formation of strontium titanate bicrystals

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with one twist grain boundary. This apparatus utilizes high uniaxial pressure and a pulsed direct current for rapid consolidation of material. Diffusion bonding of strontium titanate bicrystals without fracture, in a spark plasma sintering apparatus, is possible at high pressures due to the unusual temperature dependent plasticity behavior of strontium titanate. We demonstrate a method for the successful formation of bicrystals at accelerated time scales and lower temperatures in a spark plasma sintering apparatus compared to bicrystals formed by conventional diffusion bonding parameters. Bond quality was verified by scanning electron microscopy. A clean and atomically abrupt interface containing no secondary phases was observed using transmission electron microscopy techniques. Local changes in bonding across the boundary was characterized by simultaneous scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy.

Bonding temperature, time, and misorientation angle were all altered to determine optimum parameters needed for the maximum possible bonded interface fraction of the STO bicrystal (Table 1). The interface was considered &#39;bonded&#39; when the grain boundary was not visible during SEM imaging (Figure 2a). A &#39;non-bonded&#39; interface was exhibited when a dark image contrast or voids were present at the boundary location (Figure 2b)....

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Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals

A viable technique for the formation of strontium titanate bicrystals at high pressure and fast heating rate via the spark plasma sintering apparatus is developed.

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with ...

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Universidad de Cartagena UDEC

Research

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9.8K Views.  University of California, Davis. A viable technique for the formation of strontium titanate bicrystals at high pressure and fast heating rate via the spark plasma sintering apparatus is developed. 

Video: Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals

Fabrication of Spatially Confined Complex Oxides

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from the inherent strong electron correlations that reside within them. These materials can also possess electronic phase separation in which regions of vastly different resistive and magnetic behavior can coexist within a single crystal alloy material. By reducing the scale of these materials to length scales at and below the inherent size of the electronic domains, novel behaviors can be exposed. Because of this and the fact that spin-charge-lattice-orbital order parameters each involve correlation lengths, spatially reducing these materials for transport measurements is a critical step in understanding the fundamental physics that drives complex behaviors. These materials also offer great potential to become the next generation of electronic devices 1-3. Thus, the fabrication of low dimensional nano- or micro-structures is extremely important to achieve new functionality. This involves multiple controllable processes from high quality thin film growth to accurate electronic property characterization. Here, we present fabrication protocols of high quality microstructures for complex oxide manganite devices. Detailed descriptions and required equipment of thin film growth, photo-lithography, and wire-bonding are presented.

We describe the use of pulsed laser deposition (PLD), photolithography and wire-bonding techniques to create micrometer scale complex oxides devices. The PLD is utilized to grow epitaxial thin films. Photolithography and wire-bonding techniques are introduced to create practical devices for measurement purposes.

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from ...

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO3 (001) and DyScO3 (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca2Nb3O10- nanosheets were used, prepared by delamination of their layered parent compound HCa2Nb3O10. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.

Various procedures are outlined to prepare atomically defined templates for epitaxial growth of complex oxide thin films. Chemical treatments of single crystalline SrTiO3 (001) and DyScO3 (110) substrates were performed to obtain atomically smooth, single terminated surfaces. Ca2 Nb3 O10- nanosheets were used to create atomically defined templates on arbitrary substrates.

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain ...

Chemistry

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3.

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

A protocol for the synthesis and processing of polycrystalline SrTiO3 ceramics doped non-uniformly with Pr is presented along with the investigation of their thermoelectric properties.

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma ...

Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and conformality by taking advantage of self-limiting reactions between vapor-phase precursors and the growing film. Perovskite oxides present potential for next-generation electronic materials, but to-date have mostly been deposited by physical methods. This work outlines a method for depositing SrTiO3 (STO) on germanium using ALD. Germanium has higher carrier mobilities than silicon and therefore offers an alternative semiconductor material with faster device operation. This method takes advantage of the instability of germanium's native oxide by using thermal deoxidation to clean and reconstruct the Ge (001) surface to the 2&#215;1 structure. 2-nm thick, amorphous STO is then deposited by ALD. The STO film is annealed under ultra-high vacuum and crystallizes on the reconstructed Ge surface. Reflection high-energy electron diffraction (RHEED) is used during this annealing step to monitor the STO crystallization. The thin, crystalline layer of STO acts as a template for subsequent growth of STO that is crystalline as-grown, as confirmed by RHEED. In situ X-ray photoelectron spectroscopy is used to verify film stoichiometry before and after the annealing step, as well as after subsequent STO growth. This procedure provides framework for additional perovskite oxides to be deposited on semiconductors via chemical methods in addition to the integration of more sophisticated heterostructures already achievable by physical methods.

This work details the procedures for the growth and characterization of crystalline SrTiO3 directly on germanium substrates by atomic layer deposition. The procedure illustrates the ability of an all-chemical growth method to integrate oxides monolithically onto semiconductors for metal-oxide semiconductor devices.

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and ...

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) scaffolds with tunable specific surface areas up to 80 m2&#183;g-1. An aqueous solution of a zirconium salt, yttrium salt, and glucose is mixed with propylene oxide (PO) to form a gel. The gel is dried under ambient conditions to form a xerogel. The xerogel is pressed into pellets and then sintered in an argon atmosphere. During sintering, a YSZ ceramic phase forms and the organic components decompose, leaving behind amorphous carbon. The carbon formed in situ serves as a hard template, preserving a high surface area YSZ nanomorphology at sintering temperature. The carbon is subsequently removed by oxidation in air at low temperature, resulting in a porous, nanostructured YSZ scaffold. The concentration of the carbon template and the final scaffold surface area can be systematically tuned by varying the glucose concentration in the gel synthesis. The carbon template concentration was quantified using thermogravimetric analysis (TGA), the surface area and pore size distribution was determined by physical adsorption measurements, and the morphology was characterized using scanning electron microscopy (SEM). Phase purity and crystallite size was determined using X-ray diffraction (XRD). This fabrication approach provides a novel, flexible platform for realizing unprecedented scaffold surface areas and nanomorphologies for ceramic-based electrochemical energy conversion applications, e.g. solid oxide fuel cell (SOFC) electrodes.

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels

A protocol for fabricating porous, nanostructured yttria-stabilized-zirconia (YSZ) scaffolds at temperatures between 1,000 &#176;C and 1,400 &#176;C is presented.

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) ...

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Although electrostatic mechanisms have been proposed in the past to describe the existence of this critical thickness, the importance of chemical defects has been recently accentuated. Here, we describe the growth of metal/LAO/STO heterostructures in an ultra-high vacuum (UHV) cluster system combining pulsed laser deposition (to grow the LAO), magnetron sputtering (to grow the metal) and X-ray photoelectron spectroscopy (XPS). We study step by step the formation and evolution of the q2DES and the chemical interactions that occur between the metal and the LAO/STO. Additionally, magnetotransport experiments elucidate on the transport and electronic properties of the q2DES. This systematic work not only demonstrates a way to study the electrostatic and chemical interplay between the q2DES and its environment, but also unlocks the possibility to couple multifunctional capping layers with the rich physics observed in two-dimensional electron systems, allowing the fabrication of new types of devices.

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

We fabricate metal/LaAlO3/SrTiO3 heterostructures using a combination of pulsed laser deposition and in situ magnetron sputtering. Through magnetotransport and in situ X-ray photoelectron spectroscopy experiments, we investigate the interplay between electrostatic and chemical phenomena of the quasi two-dimensional electron gas formed in this system.

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide ...

Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its well-balanced ferroelectricity, piezoelectricity, and dielectric constant. In addition, BT does not contain any toxic elements. Therefore, it is considered to be an eco-friendly material, which has attracted considerable interest as a replacement for lead zirconate titanate (PZT). However, bulk BT loses its ferroelectricity at approximately 130 &#176;C, thus, it cannot be used at high temperatures. Because of the growing demand for high-temperature ferroelectric materials, it is important to enhance the thermal stability of ferroelectricity in BT. In previous studies, strain originating from the lattice mismatch at hetero-interfaces has been used. However, the sample preparation in this approach requires complicated and expensive physical processes, which are undesirable for practical applications.
In this study, we propose a chemical synthesis of a porous material as an alternative means of introducing strain. We synthesized a porous BT thin film using a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles were used as an organic template. Through a series of studies, we clarified that the introduction of pores had a similar effect on distorting the BT crystal lattice, to that of a hetero-interface, leading to the enhancement and stabilization of ferroelectricity. Owing to its simplicity and cost effectiveness, this fabrication process has considerable advantages over conventional methods.

Here, we present a protocol for the synthesis of porous barium titanate (BaTiO3) thin film by a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles are used as an organic template.

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its ...

Fused Filament Fabrication (FFF) of Metal-Ceramic Components

Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with diverse customization options and favorable production methods is increasing continuously. With fused filament fabrication (FFF), it is possible to produce large and complex components quickly with high material efficiency. In FFF, a continuous thermoplastic filament is melted in a heated nozzle and deposited below. The computer-controlled print head is moved in order to build up the desired shape layer by layer. Investigations regarding printing of metals or ceramics are increasing more and more in research and industry. This study focuses on additive manufacturing (AM) with a multi-material approach to combine a metal (stainless steel) with a technical ceramic (zirconia: ZrO2). Combining these materials offers a broad variety of applications due to their different electrical and mechanical properties. The paper shows the main issues in preparation of the material and feedstock, device development, and printing of these composites.

Fused Filament Fabrication FFF of Metal-Ceramic Components

This study shows multi-material additive manufacturing (AM) using fused filament fabrication (FFF) of stainless steel and zirconia.

Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with ...

Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (Cu variant) entropy-stabilized oxides. Phase pure and chemically homogeneous (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) ceramic pellets are synthesized and used in the deposition of ultra-high quality, phase pure, single crystalline thin films of the target stoichiometry. A detailed methodology for the deposition of smooth, chemically homogeneous, entropy-stabilized oxide thin films by pulsed laser deposition on (001)-oriented MgO substrates is described. The phase and crystallinity of bulk and thin film materials are confirmed using X-ray diffraction. Composition and chemical homogeneity are confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The surface topography of thin films is measured with scanning probe microscopy. The synthesis of high quality, single crystalline, entropy-stabilized oxide thin films enables the study of interface, size, strain, and disorder effects on the properties in this new class of highly disordered oxide materials.

The synthesis of high quality bulk and thin film (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O entropy-stabilized oxides is presented.

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and ...

Radio Frequency Magnetron Sputtering of GdBa2Cu3O7&#8722;&#948;/ La0.67Sr0.33MnO3 Quasi-bilayer Films on SrTiO3 (STO) Single-crystal Substrates

Here, we demonstrate a method of coating ferromagnetic La0.67Sr0.33MnO3 (LSMO) nanoparticles on (001) SrTiO3 (STO) single-crystal substrates by radio frequency (RF) magnetron sputtering. LSMO nanoparticles were deposited with diameters from 10 to 20 nm and heights between 20 and 50 nm. At the same time, (Gd) Ba2Cu3O7&#8722;&#948; ((Gd) BCO) films were fabricated on both undecorated and LSMO nanoparticle decorated STO substrates using RF magnetron sputtering. This report also describes the properties of GdBa2Cu3O7&#8722;&#948;/ La0.67Sr0.33MnO3 quasi-bilayer films structures (e.g., crystalline phase, morphology, chemical composition); magnetization, magneto-transport, and superconducting transport properties were also evaluated.

Radio Frequency Magnetron Sputtering of GdBa2Cu3O7ÃƒÆ’Ã‚Â¢Ãƒâ€¹Ã¢â‚¬Â 'ÃƒÆ’Ã…Â½ Â´/ La0.67Sr0.33MnO3 Quasi-bilayer Films on SrTiO3 STO Single-crystal Substrates

Here, we present a protocol to grow LSMO nanoparticles and (Gd) BCO films on (001) SrTiO3 (STO) single-crystal substrates by radio frequency (RF)-sputtering.

Here, we demonstrate a method of coating ferromagnetic La0.67Sr0.33MnO3 (LSMO) nanoparticles on (001) SrTiO3 (STO) single-crystal substrates by radio ...

Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals

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