Characterization of strain relaxation of (0 0 1) oriented SrTiO3 thin films grown on LaAIO3 (1 1 0) by means of reciprocal space mapping using x-ray diffraction

The strain relaxation of SrTiO₃ r.f. magnetron sputter-deposited thin films on LaAlO₃ substrates have been studied by x-ray diffraction mapping. An investigation of different x-ray optics shows that a, so called, hybrid mirror monochromator in combination with a triple-bounce analyser crystal provides very good conditions for characterization of thin distorted films grown epitaxially onto substrates with high structural order. The in-plane and out-of-plane lattice parameters of the SrTiO₃ films could accurately be determined since the x-ray diffraction optics enabled the splitting of substrate peaks, caused by the twinning in the rhombohedral LaAlO₃ to be resolved and, provided film peak intensities are high enough, to precisely establish their positions. Films in the thickness range 9.3–144.0 nm were found to be partially relaxed, having a tetragonal distortion due to in-plane strain that was found to decrease with increasing film thickness, approaching an undistorted SrTiO₃ lattice parameter of 0.3927 nm. This value is 0.6% larger than the bulk indicating that the compositions of the films were slightly non-stoichiometric. The strain relaxation of the grown films was found to follow the general trend of a predicted strain–thickness relation based on energy density balance considerations regarding misfit dislocations and lattice strain.     

Impact of epitaxial strain on the ferromagnetic transition temperature of SrRuO3 thin films

Epitaxially strained SrRuO₃ films were grown on SrTiO₃, DyScO₃, and NdGaO₃ oxide substrates using liquid-delivery metal-organic chemical vapour deposition. Temperature dependent resistivity measurements showed a shift in the Curie temperature (T_C) of the ferromagnetic phase transition which is suggested to be caused by the incorporated elastic lattice strain in the films. T_C increased with tensile and decreased with compressive strain, which was inferred from high resolution x-ray diffraction measurements of the in-plane and out-of-plane lattice parameters.     

Effect of Trivalent Ion Substitution on the Physical Properties of M-Type Hexagonal Ferrites

Aluminum-substituted barium hexagonal ferrite particles BaAl _x Fe_12-x O₁₉ with 0 ≤ x ≤ 3.5 have been prepared by solid state reaction method. The qualitative phase analysis of studied powder samples and the morphology of powders after milling were determined using the x-ray diffraction method and scanning electron microscopy, respectively. The barium hexagonal ferrite phase appeared to be the main component of the samples. The crystal size of BaFe₁₂O₁₉ phase is above 25 nm. The scanning electron microscopy images showed irregular shape and size of powder particles. According to the analytical method findings, the type of crystal lattice was confirmed to be hexagonal and the parameters of unit cell volume and x-ray density were determined. It is shown that such parameters decrease with increasing Al substitution from 699.019 to 696.702 Å³ and 5.258 to 4.828 gm/Cm³, respectively. The values of lattice parameters, grain size, microstrain, and dislocation density of all samples were calculated. The c/a value obtained from the x-ray indicates that notable changes of the atomic lattice anisotropy were induced by the Al-substitution and preheat treatments. Characteristics such as the interchain distance and interplanar distance parameter, which were obtained in the analytical method calculations, decrease with increasing Al substitution, in addition to the fact that they are related to the binding energy.     

Titanium borides prepared by self-propagating high-temperature synthesis

Ti₂B₅, TiB₁₂, TiB_≃25, TiB_≃55, and TiB_≃100 were prepared by self-propagating high-temperature synthesis and characterized by microstructural analysis, x-ray diffraction, and x-ray microanalysis. Data on the crystal structure, lattice parameters, and mechanical properties of the synthesized borides are presented.     

Preparation, Structure, and Thermal Expansion of CuIn3Se5

Homogeneous CuIn₃Se₅crystals 12 mm in diameter and up to 40 mm in length, with a tetragonal defect-chalcopyrite structure were grown by directional solidification. The structural parameters and thermal expansion of the crystals were measured by x-ray diffraction between 90 and 650 K. Throughout the temperature range studied, the c-axis thermal expansion coefficient of CuIn₃Se₅was found to be much smaller than the a-axis one.     

Crystal chemistry of REVO3 phases (RE = La-Lu,Y)

All REVO₃ phases have been prepared and characterized by x-ray powder diffraction for symmetry and unit cell parameters. LaVO₃ and CeVO₃ have tetragonal variations of the perovskite structure while all remaining REVO₃ phases are orthorhombic and isostructural with GdFeO₃. The variation of cell parameters with RE³⁺ ionic radius shows a steady contraction with decreasing radius for a_o, c_o and V while b_o goes through a maximum.     

High-Pressure Phase Transitions of LaF3and CeF3

The effect of high pressure on the structure of LaF₃ (tysonite), CeF₃, and nonstoichiometric LaF₃-based solid solutions (rhombohedral system, P c1, Z = 6) is discussed. In the systems MF₂–LaF₃ with M = Pb and Sr, fluorite-like M_{1 –x} La _x F_{2 + x} solid solutions (Fm3m, Z = 4) are obtained in the composition range 0.5 x 0.75 by quenching from 1500–1700 K at p = 10 GPa. By extrapolating the composition dependences of the lattice parameter for these cubic solid solutions, the lattice parameter of cubic LaF₃ is estimated at a= 5.86 ± 0.02 Å. High-pressure x-ray diffraction studies indicate that CeF₃ undergoes a first-order phase transition similar to that revealed recently in LaF₃. At p = 20.6 GPa, the lattice parameters of orthorhombic CeF₃ (Cmma, Z= 8) are a = 8.062 ± 0.006 Å, b = 8.457 ± 0.009 Å, and c = 5.091 ± 0.006 Å. The transition is accompanied by a 7.3% decrease in volume. The high-pressures structure of LaF₃ and CeF₃ can be thought of as a distorted modification of the structure of a hypothetical fluorite-like trifluoride. The lattice parameters of the orthorhombic and cubic cells are related by a _ortho b _ortho a _cubic and c _ortho a _cubic.     

Synthesis and Properties of Ln3Ti2TaO11Mixed-Layer Perovskite-like Compounds

The Ln₃Ti₂TaO₁₁(Ln = La, Pr) compounds (A _n B _n O_{3n+ 2}family) with noncentrosymmetric layered perovskite-like structures were prepared by heat-treating coprecipitated hydroxides, and their lattice parameters and density were determined. The structural changes accompanying the formation of these compounds were studied. Analysis of x-ray diffraction data indicated that, in the structures of Ln₃Ti₂TaO₁₁, the LnTaO₄and Ln₂Ti₂O₇perovskite layers are stacked in an ordered manner. The spontaneous polarization in Ln₃Ti₂TaO₁₁was evaluated.     

X-ray Diffraction Study of the Structure and Defect System of Nominally Pure and Er<Superscript>3+</Superscript>- and Ce<Superscript>3+</Superscript>-Activated (Na<Subscript>0.5</Subscript>La<Subscript>0.5</Subscript>)MoO<Subscript>4</Subscript> Crystals

Nominally pure and activated (Er³⁺ and Er³⁺ + Ce³⁺) sodium lanthanum molybdate single crystals grown by the Czochralski technique from the (Na_0.5La_0.5)MoO₄ melt in different environments and then oxidized in air at 100°C are characterized in detail by x-ray diffraction (lattice parameters and structure refinement by the Rietveld method and single-crystal techniques). The results confirm that (Na_0.5La_0.5)MoO₄ crystallizes in a tetragonal scheelite structure (sp. gr. I₁/a). The crystals (especially unannealed crystals grown in neutral atmosphere) are shown to contain oxygen vacancies. In addition, some of the samples contain Mo vacancies. The Er³⁺ distribution over some of the activated crystals is highly inhomogeneous. As a result, the crystals contain Er-enriched zones with a distorted scheelite structure.     

Perovskite formation and dielectric responses in Pb(Zn1/3Nb2/3)O3-modified Pb(Zn1/3Ta2/3)O3-PbTiO3 ceramics

Pb(Zn_1/3Ta_2/3)O₃-PbTiO₃ ceramic compositions were modified by the introduction of Nb to the octahedral lattice sites. Resultant tendencies in the perovskite formation and dielectric properties were examined. System powders were prepared using a B-site precursor method. Developed structures and lattice parameters of the system compositions were investigated by powder X-ray diffractometry, from which the parameter of a hypothetical perovskite Pb(Zn_1/3Ta_2/3)O₃ is proposed. Weak-field low-frequency dielectric responses of the system ceramics were measured.     

Crystal Growth and Structure of the Zn<Subscript>0.97</Subscript>Cd<Subscript>0.03</Subscript>As<Subscript>2</Subscript> Solid Solution

Single crystals of the Zn_0.97Cd_0.03As₂ solid solution are prepared, and their structure is determined by x-ray diffraction. The incorporation of Cd into ZnAs₂ has no effect on its lattice parameters (to within the error of determination). Cd is shown to occupy interstitial sites in the solid solution.     

Structural Instability and Internal Stress in Mechanically Activated Alkaline-Earth Peroxides

The effect of mechanical activation on the structural properties of CaO₂ is studied by x-ray diffraction. Mechanical activation for a certain time is shown to produce sharp changes in the width of diffraction peaks from CaO₂ and its lattice parameters.     

Solid electrolytes based on Na3PO4 doped with S,Se, Mo,W

The cubic form of Na₃PO₄ forms extensive ranges of solid solutions, which are stable from room temperature to the melting point, by the replacement mechanism, Na + P = Y : Y = S, Se, Mo, W. In all four cases, the conductivity increases markedly with increasing Y content and is attributed to the increase in number of mobile sodium ion vacancies. Partial phase diagrams, lattice parameters and conductivity Arrhenius parameters are given for each system     

LaNi5- and RT3-based (R = Ce, Nd, Gd, Er; T = Co, Ni, Fe) hydrides prepared at low temperatures and H2 pressures

Hydride phases based on the intermetallic compounds LaNi₅, CeCo₃, NdNi₃, GdFe₃, DyCo₃, and ErNi₃ have been synthesized at a hydrogen pressure of 10 MPa and a temperature of 273 K. The phase composition of the synthesized materials and the lattice parameters of the hydride phases have been determined by X-ray diffraction. During storage in air at room temperature, the hydrides decompose more slowly than do their analogs synthesized at low pressure. The hydrogen content of the hydrides is higher than or similar to that of hydride phases synthesized at high pressure. X-ray diffraction results for the low-temperature RT₃-based intermetallic hydrides demonstrate that their lattice is expanded to a lesser extent than that of their high-pressure analogs.     

Structural,Thermal, and Electrical Study of Bi0.5Sr0.5MnO3

Solid oxide fuel cell (SOFC) is considered as a potential candidate for clean and efficient alternate energy source. Efforts are being made to reduce their operating temperature for SOFCs commercialization. However, the reduction in operating temperature increases the polarization effect in the existing cathodes. In the present study, Bi_0.5Sr_0.5MnO₃ was synthesized and studied for its structural, thermal, and electrical properties. Bi_0.5Sr_0.5MnO₃ was synthesized by conventional solid state reaction method. The as-prepared sample was characterized by x-ray diffraction, scanning electron microscope, thermogravimetric analysis, dilatometer and impedance spectroscopy. The Rietveld refinement results confirm that Bi_0.50Sr_0.50MnO₃ shows the tetragonal symmetry with p4 mm space group. Scanning electron microscopy study shows that the distribution of grains is uniform and the grains are well connected to each other due to better sinterability of the samples. The dilatometric curve shows linear behavior up to 600°C and after that becomes steeper. This can be due to the loss of lattice oxygen at higher temperatures and creation of oxygen vacancies. The thermal expansion coefficient of the system is ～8.9 × 10^?6 °C^?1 and total conductivity of the sample is ～4.78 × 10^?3 S/cm.     

Crystallographic and dielectric properties of barium-substituted Pb(Mg1/3Ta2/3)O3 ceramics

Ceramic powders of (Ba,Pb)Pb(Mg_1/3Ta_2/3)O₃ were prepared via a B-site precursor route. Crystal symmetries and lattice parameters were determined. Monophasic perovskite was developed after the two-step reaction process, in which the lattice parameters showed linear changes in the entire composition range. Dielectric responses of the ceramics with compositional and frequency changes were investigated. The results were also compared with the (Ba,Pb)(Zn_1/3Ta_2/3)O₃ data.     

Growth and X-ray Diffraction Study of YCa4O(BO3)3:Ce,Er,Yb Crystals

YCa₄O(BO₃)₃crystals (sp. gr. Cm), nominally pure and activated with Yb, Er, and/or Ce, were grown by the Czochralski technique. The crystal structure of YCa₄O(BO₃)₃was refined by single-crystal x-ray diffraction, and the site compositions were determined: (Y_0.792Ca_0.208(6))(Ca_0.938Y_0.062(4))₂Ca₂O_0.96(2)[ ]_0.04(BO₃)₃([ ] = vacancy). The data set for YCa₄O(BO₃)₃was found to contain additional reflections which were inconsistent with space group Cmbut could be indexed in a cell with doubled a. No superlattice reflections were detected in the case of the activated crystals. Structural data for LnCa₄O(BO₃)₃were used to derive relations for the lattice parameters and average cation–anion distances as functions of r _Lnand weighted-average cation radii on the mixed-occupancy sites, which made it possible to assess the distributions of Y, Yb, Er, Ce, and Ca over the mixed-occupancy sites. Absolute structure determination showed that the pure and Yb³⁺-activated YCa₄O(BO₃)₃crystals differed in polarity.     

Preparation,cell constants,and some magnetic properties of CeScO3

CeScO₃ was prepared for the first time by arc-melting appropriate amounts of CeO₂, Sc₂O₃, and Sc. The x-ray powder pattern was indexed on an orthorhombic, GdFeO₃-type cell, with cell constants (A°) a = 5.787(3), b = 8.047(8), c = 5.626(4). Magnetic susceptibility data on powdered samples from 4.2K to 300K were obtained. The data do not obey the Curie-Weiss Law in this temperature range and this behaviour is ascribed to crystal field effects. Two models for the crystal field intensity parameters, B^k_q, were tested by comparing calculated and experimental susceptibilities. One model gave a fair fit to the high temperature susceptibility and a ground state powder averaged 〈geff〉 = 2.02 in fair agreement with the experimental 〈geff〉 = 2.07. The implications for these results on CeScO₃ for the isostructural material, CeTiO₃, are discussed.     

Properties of AgGa x In1 – x Se2 Solid Solutions

AgInSe₂, AgGaSe₂, and AgGa _x In_{1 – x} Se₂ crystals consisting of large blocks were grown by the horizontal Bridgman process, and their composition and lattice parameters were determined by electron probe x-ray microanalysis and x-ray diffraction. The lattice parameters of the solid solutions were shown to vary linearly with x. Differential thermal analysis was used to determine the phase-transition temperatures of the crystals and to map out the AgInSe₂–AgGaSe₂ phase diagram, which was also evaluated thermodynamically. The density of the AgGa _x In_{1 – x} Se₂ solid solutions was found to vary linearly with composition, while their microhardness shows a maximum.     

X-ray diffraction study of nonstoichiometry in CuInSe2 + §

CuInSe₂ alloys with the stoichiometric Cu : In ratio and varying Se content were studied by x-ray diffraction. The lattice parameters of the alloys, atomic positional parameterx, and the bond lengths lcu-se and l_in-Se were determined. The lattice parameters were found to increase with decreasing Se content on the Se-poor side of CuInSe₂ and to pass through a flat minimum around 50.5 at. % Se. The results are interpreted as indicating that the dominant intrinsic defects in Se-deficient CuInSe₂ are Cu interstitials. In the Se-enriched alloys containing more than ≃50.5 at. % Se, the dominant defects are cation vacancies, Se interstitials, and/or Se_Cu and Se_In antisite defects.