Pole Figure Analysis Research Articles

Effects of heat treatment and film thickness on microstructure and critical properties of YBCO film processed by TFA-MOD

We fabricated YBCO film on an LAO substrate using the TFA-MOD method and evaluated the effects of the heat treatment temperature and film thickness on the microstructure, degree of texture, and critical properties. The calcining and firing processes were performed in the temperature ranges of 370–460°C and 750–800°C, respectively. We found that the phase purity, grain size and orientation, and degree of texture varied with the calcining and firing temperatures.The films fired at 775°C after calcining at 400–430°C showed the highest critical temperature (TC-onset) of 89.5K and critical current (IC) of 40A/cm-width, which corresponds to a critical current density (JC) of 1.8MA/cm2. According to the XRD, pole-figure, SEM images, and Raman analysis, these highest critical properties are probably due to the formation of a purer YBCO phase and stronger biaxial texture. In the multi-coated films, the IC value increased from 39 to 169A/cm-width as the number of coatings increased from one to four, while the corresponding JC was measured to be in the range of 0.8–1.2MA/cm2. Both the IC and JC decreased when a further coating was applied due to the degradation of the microstructure.

Precursor Evolution and Nucleation Mechanism of YBa2Cu3Ox Films by TFA Metal−Organic Decomposition

We describe the conversion of yttrium, barium, and copper trifluoracetate-derived solid precursors to epitaxial YBa2Cu3Ox superconducting ceramics on (001)-oriented LaAlO3 substrates. Transmission electron microscopy, electron energy loss spectroscopy, energy-dispersive X-ray analysis, and X-ray diffraction are used to characterize the reaction path and nucleation mechanism yielding high critical current YBa2Cu3O7. Our results show that the pyrolysis of the trifluoracetate solutions yields a nanostructured, partially amorphous Ba1-xYxF2+x matrix having a Ba/Y ratio close to 2, with homogeneously dispersed CuO nanoparticles. Upon heating, the chemical trajectory of the fluoride matrix and the overall microstructural evolution of the ceramic precursor prior to YBa2Cu3O7 nucleation is driven by the decomposition and oxidation of this solid solution. The Y solid solubility decreases with temperature yielding Y2O3 which reacts with the CuO particles forming Y2Cu2O5 at about 700 °C. In addition, electron energy loss spectroscopy reveals a high oxygen concentration and almost no Y in the matrix quenched from 795 °C, at a stage where the YBa2Cu3Ox phase still forms disconnected 50−100 nm thick islands spaced by 1−2 μm. The observed evolution from Ba1-xYxF2+x to a barium oxyfluoride mostly occurs prior to the heteroepitaxial nucleation of YBa2Cu3Ox at about 700 °C. Hence, a microstructural scenario is defined which favors competitive nucleation growth between heteroepitaxial YBa2Cu3Ox and bulk Y2Cu2O5. X-ray diffraction pole-figure analysis reveals that the oxyfluoride phase is heavily textured, exhibiting two epitaxial relationships with the (001)-LaAlO3 substrate: (001)OF//(001)LaAlO3, [110]OF//[100]LaAlO3 and (111)OF//(001)LaAlO3, [110]OF//[100]LaAlO3 (OF stands for oxyfluoride). High-resolution observations of the growth front support that (111)-oriented oxyfluoride regions provide low-barrier nucleation sites for c-axis-oriented YBa2Cu3Ox on the buried (001)-LaAlO3 substrate. However, owing to its high mismatch, this orientation only represents roughly 15% percent of the total OF volume. Considering that the nucleation of YBa2Cu3Ox is confined to those regions, this would lead to an anomalously large internuclei spacing, as is indeed observed, favoring the formation of large YBa2Cu3Ox grains and films with a low mosaic spread.

Synthesis of b‐Oriented TS‐1 Films on Chitosan‐Modified α‐Al2O3 Substrates

The controllable orientation of TS-1 crystals on a porous alumina substrate is achieved by using a thin chitosan film as a structure-directing matrix. A single layer of TS-1 crystal grains is fully b-oriented. The crystal grains in a multilayer TS-1 film are preferentially b-oriented (ca. 70%) according to XRD and pole figure analyses (see figure). The obtained membrane shows strong selectivity in an oxidation-catalysis experiment.

Room temperature epitaxial growth of TiN on SiC

Epitaxial growth of a titanium nitride (TiN) on (6H)-SiC (0001) is achieved at room temperature by means of direct current magnetron sputtering. The epitaxial relationship is established by X-ray pole figure and Φ-scan. Cross-sectional transmission electron microscopy and pole figure analysis show that the orientation relationship is ( 111 ) TiN ‖ ( 0001 ) SiC [ 0 1 ¯ 1 ] TiN ‖ [ 1 2 ¯ 10 ] SiC , It is different from that on sapphire, “ ( 111 ) TiN ‖ ( 0001 ) Al 2 O 3 [ 10 1 ¯ ] TiN ‖ [ 10 1 ¯ 0 ] Al 2 O 3 ” , in spite of the same crystal structure of substrate surfaces. Different lattice mismatch is a plausible explanation.

EBSP measurements of hydrogenated Zircaloy-2 claddings with stress-relieved and recrystallized annealing conditions

Precipitation behavior of zirconium hydrides and microscopic texture in three kinds of Zircaloy-2 fuel claddings with stress-relieved and recrystallized annealing conditions have been examined by electron backscattering diffraction patterns (EBSP). The microscopic texture data obtained by EBSP were consistent with the macroscopic X-ray data. The zirconium basal plane was observed to have a more radial texture in the case of the recrystallized tube as compared to the stress-relieved tube, even though both tubes had the same tube reduction path. In the recrystallized tubes, the frequency of precipitation and stable growth sites in inter-granular hydrides were about twice as high as that in intra-granular sites. In the stress-relieved tubes, this value was not calculated because of the almost equivalent sizes of hydrides and smaller zirconium matrix grains. The observation frequency of the habit planes of hydrides, which was statistically derived based on pole figure analysis of EBSP between hydrides and surrounding zirconium matrix grains, decreased in the order (0 0 0 1) α ∥{1 1 1} δ ≫ {1 0 1 ¯ 7} α ∥{1 1 1} δ > {1 0 1 ¯ 1} α ∥{1 1 0} δ .

Development of textured substrates with high strength and weak magnetism

Ni-clad substrates for HTS coated conductors have been developed to enhance their mechanical strength and to reduce their magnetization. The Ni-clad substrate has a sandwich structure, which comprises two pure Ni layers at the top and bottom sides and a Ni–Mo alloy layer at the center.The textured Ni-clad substrate shows a 0.2% proof stress of 1.1GPa, which is 25 times higher than that of the textured pure Ni substrate. The saturated magnetization is about half that of pure Ni substrate, which reduces the magnetic loss of the substrate remarkably. In order to evaluate bi-axially textured growth of the buffer layers on the substrate, a CeO2 buffer layer was deposited by electron-beam evaporation. The X-ray diffraction and pole figure analysis of the CeO2 buffer layer indicate that the buffer layer has the {200}〈220〉 cube orientation.A 40m-long Ni-clad substrate has been successfully fabricated to demonstrate the mass-productivity. The 40m-substrate exhibits that the orientation is a good alignment and the quality is homogeneous over the full length.The Ni-clad substrate is expected to be one of the useful substrates for HTS coated conductors.

Misfit strain relaxation in (Ba0.60Sr0.40)TiO3 epitaxial thin films on orthorhombic NdGaO3 substrates

Strain relaxation in (Ba0.60Sr0.40)TiO3 (BST) thin films on ⟨110⟩ orthorhombic NdGaO3 substrates is investigated by x-ray diffractometry. Pole figure analysis indicates a [010]BST∥[1¯10]NGO and [001]BST∥[001]NGO in-plane and [100]BST∥[100]NGO out-of-plane epitaxial relationship. The residual strains are relaxed at h∼200nm, and for h>600nm, films are essentially strain free. Two independent dislocations mechanisms operate to relieve the anisotropic misfit strains along the principal directions. The critical thickness for misfit dislocation formation along [001] and [010] are 11 and 15nm, respectively. Stress analysis indicates deviation from linear elasticity for h<200. The films with 10<h<25nm are of monoclinic symmetry due to a finite principal shear stress along [110] of the initial orthorhombic cell.

Substrate effect on the temperature coefficient of resistance of La0.7Ca0.3MnO3 thin films prepared by metal organic deposition

Epitaxial La0.7Ca0.3MnO3 (LCMO) thin films were successfully prepared by the metal-organic deposition process on various (001) single-crystal substrates: MgO, LaAlO3 (LAO), SrTiO3 (STO), and (LaAlO3)0.3-(SrAlTaO6)0.7 (LSAT). The crystallinity and the epitaxial growth of the LCMO films were characterized by X-ray diffraction (θ − 2θ scans and pole-figure analysis). The temperature dependence of the resistance of the LCMO/LSAT, LCMO/STO and LCMO/LAO films exhibit typical characteristics with a transition from the paramagnetic-insulator state to the ferromagnetic-metallic state at a temperature peak (Tp) ranging from 258 to 270 K. However, the LCMO/MgO films exhibited a semiconducting behavior without any transition. Based on the R(T) measurement, we calculated the temperature coefficient of resistance (TCR) for a bolometric application and we obtained 22%/K, 10.2%/K and 27.5%/K for the film grown on the LSAT, STO and LAO substrates, respectively. This difference in the TCR properties is related to the strain induced by the lattice mismatch between LCMO and the different substrates.

Effect of {0 0 1}〈1 1 0〉 texture on superelastic strain of Ti–Nb–Al biomedical shape memory alloys

Anisotropy in recovery strains was examined in a Ti–Nb–Al superelastic β-Ti alloy with a well-developed {0 0 1} β〈1 1 0〉 β texture. An ingot of Ti–24 mol% Nb–3 mol% Al alloy was fabricated by arc melting, homogenized at 1273 K for 7.2 ks, cold-rolled with 99% reduction in thickness and then solution-treated at 873 K for 3.6 ks. X-ray diffraction pole figure and electron backscatter pattern analysis revealed that {0 0 1} β〈1 1 0〉 β texture with grain size of 2 μm was developed in the alloy under the condition of the above thermo-mechanical treatment. Cyclic loading-unloading tensile test was made to evaluate superelastic properties. Tensile specimens were made with various orientation between the rolling direction (RD) and the longitudinal direction. Superelastic strain ( ɛ SE) was measured as the sum of the transformation strain ( ɛ TR) of β–α″ thermoelastic martensitic transformation and pure elastic strain ( ɛ E). It was found that ɛ TR at ϕ = 0° and 90° was almost the same and decreased to a minimum at around ϕ = 45°. On the other hand, it was found that ɛ E increased to a maximum at around ϕ = 45°. These orientation dependences of ɛ TR and ɛ E were in good agreement with the crystallography of the transformation and the anisotropy in Young's modulus in the alloy. ɛ SE was almost a constant regardless of ϕ. It was found that anisotropy in the tensile component of the superelastic strain available along the directions lying within the normal plane can be lowered by the development of the {0 0 1} β〈1 1 0〉 β texture.

The effects of the firing temperature of YBCO coated conductors fabricated by TFA-MOD process

We fabricated YBCO films on LAO substrates using the TFA-MOD method and evaluated the effects of the heat treatment temperature on the microstructure, degree of texture, and critical properties. The phase formation and microstructure were characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy (SEM) and the degree of texture was evaluated by pole-figure analysis.The firing was performed in the temperature range of 750–800°C and we found that the phase purity, grain size and orientation, degree of texture, and oxygen content varied with the firing temperature. The films fired at 775°C showed the highest critical temperature (TC-onset) of 89.5K and critical current (IC) of 40A/cm-width, which corresponds to a critical current density (JC) of 1.8MA/cm2. According to the results of the XRD, pole-figure, SEM and Raman analyses, these optimum critical properties can probably be attributed to the formation of a pure YBCO phase, stronger c-axis orientation and higher oxygen content.

Growth Mechanism of Textured MgO Thin Films via SSCVD

Magnesium oxide thin films have been deposited with use of single source chemical vapor deposition (SSCVD). The resultant films were examined by using transmission electron microscopy, X-ray texture analysis, and pole figure analysis. Due to the nature of the chemical reactions occurring at the surface during SSCVD growth, which result in a high growth rate/low flux environment, films of (111) orientation have been achieved without an amorphous underlayer, an unusual result for films of this orientation. Moreover the films have a strong degree of biaxial texturing in the x-y plane as found with X-ray texture analysis. These findings have important implications for buffer layers in perovskite thin film devices. The mechanism producing these structures has been revealed by using TEM and is discussed here.

Laser Dressing of Alumina Grinding Wheels

High-power lasers are being explored as a non-contact-type dressing tool for alumina grinding wheels. The alumina grinding wheel surface underwent melting and/or vaporization on the surface when laser-dressed, forming a modified layer on the surface. Refinement of the grain size took place. The individual particles that formed on the surface had well-defined faceted structures. Microcutting edges were generated on the individual grains and particles, which can act as cutting edges for efficient grinding. The results of x-ray diffraction and pole figure analysis suggested that the formation of these faceted structures was due to the preferential orientation of the grains after dressing.

CrO 2 (1 0 0) and TiO 2 (1 0 0) film heteroepitaxy on a BaF 2 (1 1 1)/Si (1 0 0) substrate

Multi-domained heteroepitaxial rutile-phase TiO 2 (1 0 0)-oriented films were grown on Si (1 0 0) substrates by using a 30-nm-thick BaF 2 (1 1 1) buffer layer at the TiO 2–Si interface. The 50 nm TiO 2 films were grown by electron cyclotron resonance oxygen plasma-assisted electron beam evaporation of a titanium source, and the growth temperature was varied from 300 to 600 °C. At an optimal temperature of 500 °C, X-ray diffraction measurements show that rutile phase TiO 2 films are produced. Pole figure analysis indicates that the TiO 2 layer follows the symmetry of the BaF 2 surface mesh, and consists of six (1 0 0)-oriented domains separated by 30° in-plane rotations about the TiO 2 [1 0 0] axis. The in-plane alignment between the TiO 2 and BaF 2 films is oriented as [0 0 1] TiO 2 || BaF 2 [ 1 0 1 ¯ ] or [0 0 1] TiO 2 || BaF 2 [ 1 1 2 ¯ ] . Rocking curve and STM analyses suggest that the TiO 2 films are more finely grained than the BaF 2 film. STM imaging also reveals that the TiO 2 surface has morphological features consistent with the BaF 2 surface mesh symmetry. One of the optimally grown TiO 2 (1 0 0) films was used to template a CrO 2 (1 0 0) film which was grown via chemical vapor deposition. Point contact Andreev reflection measurements indicate that the CrO 2 film was approximately 70% spin polarized.

Texture of Ru columns grown by oblique angle sputter deposition

Ru films were sputter deposited on native oxide p-Si(100) substrates under normal incidence and oblique angle incidence with and without substrate rotation. We characterized the crystalline texture and morphology of the Ru films by x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. For the case of normal incidence, a smooth, uniform surface layer was observed, and pole figure analysis showed coexisting {101¯0}, {0002}, and {101¯1} normally oriented textures. For oblique angle incidence, we found that the films grown by uniform substrate rotation consist of isolated, vertical columnar structures with a clear pyramidal-shaped apex and display a normal {101¯0} fiber texture. Individual vertical columns were found to possess a single-crystal structure. In comparison, Ru films grown without substrate rotation possess a slanted columnar structure. They mainly show a tilted {101¯1}{101¯0} two-orientation (II-O) texture, with non-negligible {101¯0}{112¯0} and {0002} {112¯0} II-O textures as well. The formation of textures under oblique angle deposition was ascribed to the competition between crystalline planes having different vertical growth rates, where the planes associated with a higher rate survive from the shadowing effects. We argue that the vertical growth rate is determined by the atom mobility. Under substrate rotation this mobility is correlated with the overall atomic roughness of the crystalline planes. For a fixed substrate the adatom mobility exhibits anisotropic behavior, which is reflected in the biased diffusion.

Correlation between Thermoelectric Properties and Plastic Deformation of p-Type Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> Thermoelectric Materials

A plastic deformation process and ratio study of p-type Bi 0.5 Sb 1.5 Te 3 was performed. The ingots were grown by the Bridgman method. Disks were cut from the ingots and deformed by either cold-pressing or by hot-pressing under pulse current heating. The plastic deformation ratio was controlled from 55 to 90%. The crystal structures of the deformed samples were identified by X-ray diffraction and pole figure analyses. The diffraction patterns indicate that the surfaces and bottoms of the samples were highly oriented in the hexagonal (00-l) plane. Thermoelectric properties change depending on not the plastic deformation ratio but the kind of plastic deformation process. The power factor for hot-press deformed samples exceeded those for the original ingots and cold-press deformed samples. The results suggest that the process of hot-press deformation enhances the thermoelectric properties of p-type Bi 0.5 Sb 1.5 Te 3 .

P-type Bi<sub>0.5</sub>Sb<sub>1.5</sub>Te<sub>3</sub>熱電材料の熱電特性と塑性加工度との相関関係

A plastic deformation process and ratio study of p-type Bi0.5Sb1.5Te3 was performed. The ingots were grown by the Bridgman method. Disks were cut from the ingots and deformed by either cold-pressing or hot-pressing under pulse current heating. The plastic deformation ratio was controlled in the range from 55 to 90%. The crystal structures of the deformed samples were identified by X-ray diffraction and pole figure analyses. The diffraction patterns indicate that the surfaces and bottoms of the samples were highly oriented in the hexagonal (00-l) plane. Thermoelectric properties change depending on not the plastic deformation ratio but the kind of plastic deformation process. The power factor for hot-press deformed samples exceeded those for the original ingots and cold-press deformed samples. The results suggest that the process of hot-press deformation enhances the thermoelectric properties of p-type Bi0.5Sb1.5Te3.

Epitaxial Growth of ZnO Thin Films on SiC Prepared by Chemical Solution Deposition

ABSTRACTZinc oxide (ZnO) thin films have emerged as one of the most promising oxide materials owing to their optical and electrical properties, together with their high chemical and mechanical stability. Chemical solution deposition (CSD) is attractive technique for obtaining ZnO thin films and has the advantages of easy control of the film composition and easy fabrication of a larger-area thin film at low cost. In this work, epitaxial ZnO thin films on SiC substrate were prepared by using a CSD method with a zinc naphthenate precursor. Precursor films were pyrolyzed at 500°C for 10 min in air and finally annealed at 600°C, 700°C, 800°C and 900°C for 30 min in air. Crystallinity and in-plane alignment of the films were investigated by X-ray diffraction theta-2 theta scan and pole-figure analysis. Scanning electron microscope, scanning probe microscope, and He-Cd laser (325 nm) are used to detect the surface morphology and photoluminescence of the films. The effects of annealing temperature on crystallinity and epitaxy of the films will be fully discussed on the basis of the results of X-ray diffraction analysis.

Crystallography, microstructure and morphology of Mg 4Nb 2O 9/MgO and Mg 4Ta 2O 9/MgO interfaces formed by topotaxial solid state reactions

Mg 4Nb 2O 9/MgO and Mg 4Ta 2O 9/MgO interfaces of definite crystallography were formed by topotaxial thin film solid state reactions in the systems MgO–Nb 2O 5 and MgO–Ta 2O 5. MgO (0 0 1) single crystal substrates, heated to different temperatures, were subjected to Nb–O and Ta–O vapors generated by e-beam evaporation in high vacuum. Thin films mainly containing the phases Mg 4Nb 2O 9 and MgNb 2O 6, respectively Mg 4Ta 2O 9 and MgTa 2O 6, were formed by gas–solid reactions. The crystallographic relationships between the product phases and the MgO substrate were systematically studied by X-ray diffractometry and transmission electron microscopy (TEM). Surprisingly pole figure analysis revealed more than one orientation relationship for some of the phases: Mg 4Nb 2O 9 and Mg 4Ta 2O 9 grew with (1 1 .4), (1 1 .6) and (1 1 .9) orientations, depending on temperature. Selected area diffraction patterns and high resolution TEM images show that these three orientations have a common Mg 4(Nb/Ta) 2O 9 [ 1 1 ¯ .0 ] /MgO [ 1 1 ¯ 0 ] axis and differ by the angle between the Mg 4(Nb/Ta) 2O 9 (0 0 .1) and MgO (1 1 1) planes. Crystallographic illustrations of this phenomenon are given, and possible origins and consequences for the solid state reaction are discussed. Indications for two different interfacial reaction mechanisms are found.

Investigations of structure and morphology of the AlN nano-pillar crystal films prepared by halide chemical vapor deposition under atmospheric pressure

Abstract Aluminum nitride (AlN) prepared under atmospheric pressure using a halide chemical vapor deposition method has been examined by means of a variety of analytical techniques. Scanning electron microscopic observations showed that the crystals deposited onto a Si(100) substrate have hexagonal pillar structure. Based on the X-ray diffraction and X-ray pole-figure analyses, it was deduced that the each AlN pillar crystal grows with a different rotation angle around the 〈001〉 axis. Transmission electron diffraction showed that they are of single-like form. This was also confirmed by the selected area electron diffraction image as well. It was found that the diameter of pillar which constitutes an AlN film was significantly dependent upon the ratio of NH3/AlCl3 used as source materials and the growth temperature.

Thermoelectricity for crystallographic anisotropy controlled Bi–Te based alloys and p–n modules

The p-type (Bi 2Te 3) 0.2(Sb 2Te 3) 0.8 and n-type (Bi 2Se 3) 0.05(Bi 2Te 3) 0.95 alloys were fabricated by the shear extrusion to enhance texture evolution. Transverse Direction (TD) inverse pole figure analysis via electron backscattered diffraction patterns (EBSP) showed that most of the crystallographic orientations of shear-extruded sample were well aligned in the range deviating from 60° to 90° from the c-axis. The electric resistivity of p-type controlled to be 1.008 × 10 −5 Ω m, which is nearly equal to that of unidirectionally grown sample. The maximum figure of merit for p-type alloy was found to be z = 3.03 × 10 −3 K −1 and for the n-type, z = 2.26 × 10 −3 K −1. Thermoelectric p–n modules were prepared via the spark plasma sintering (SPS) solid bonding for evaluation on their thermoelectricity. The power generation characteristic of p–n modules was also evaluated for various temperature differences between cold and hot sources.