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X-ray diffraction measurements of tetragonal chalcopyrite cadmium germanium arsenide crystal are carried out over the range 25-450 °C. The collected patterns show that the powder neither yields a new phase nor structurally transforms to any other architecture. Accurate lattice parameters (including two lattice constants a and c, cell volume V, axial ratio k, and tetragonal distortion δ) are determined by means of Cohen's least square method. Polynomial fit approximation is adopted to quantitatively describe the temperature dependence of lattice parameters. These results are the groundwork that allows the evaluation of thermal expansion coefficients defined as αR = R-1(dR/dT) where R represents lattice parameters. The average thermal expansion coefficients are evaluated, 13.9 × 10-6 K-1 for αa and 2.8 × 10-6 K-1 for αc, respectively. It is also found that αa increases while αc decreases with temperature, which in consequence brings forth the large anisotropy of thermal expansion between the two main axes (a-axis and c-axis). Detailed discussion reveals that the anisotropy behavior is in tight association with the nearest neighboring bonds. Namely, the thermal expansion coefficient perpendicular to c-axis (αa) depends to a large extent on the ionic Cd-As bonds, while that parallel to c-axis (αc) depends on the covalent Ge-As bonds. Finally, the Grüneisen parameters at different temperatures are evaluated and also exhibit anisotropic behavior (γa > γc). It is found that γa is temperature-dependent and increases with temperature, while γc tends to be temperature-independent. [ABSTRACT FROM AUTHOR]

Changes in the refractive index and thickness of amorphous As2S8 semiconductor film are observed under illumination, annealing–illumination, and annealing-illumination cycles. Properties of the As2S8 film are measured using techniques of prism coupler, x-ray diffraction spectra and Raman spectra. After light illumination the refractive index change in an as-deposited As2S8 film is one order of magnitude greater than that of an annealed As2S8 film, corresponding to ∼0.06 and ∼0.0057, respectively. Photoexpansions with a change in the relative film thickness of the as-deposited and annealed As2S8 film are nearly -3.5% and -2.1%, respectively, which exhibit the photodensification. The full reversibility of the photoinduced refractive index change is claimed on an annealed As2S8 film sample. [ABSTRACT FROM AUTHOR]

We investigate the strain relaxation and surface morphology of epitaxial SrTiO3 (STO) films grown on (001)O and (110)O planes of orthorhombic NdGaO3 (NGO), and (001) plane of cubic (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates. Although the average lattice mismatches are similar, strikingly regular crosshatched surface patterns can be found on STO/NGO(001)O[(110)O] films, contrary to the uniform surface of STO/LSAT(001). Based on the orientation and thickness dependent patterns and high-resolution x-ray diffractions, we ascribe the crosshatch morphology to the anisotropic strain relaxation with possibly the 60° misfit dislocation formation and lateral surface step flowin STO/NGOfilms, while an isotropic strain relaxation in STO/LSAT. Further, we show that the crosshatched STO/NGO(110)O surface could be utilized as a template to modify the magnetotransport properties of epitaxial La0.6Ca0.4MnO3 films. This study highlights the crucial role of symmetry mismatch in determining the surface morphology of the perovskite oxide films, in addition to their epitaxial strain states, and offers a different route for designing and fabricating functional perovskite-oxide devices. [ABSTRACT FROM AUTHOR]