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The structural and magnetocaloric properties of the perovskite manganite [La.sub.2/3-x][Y.sub.x][Ca.sub.1/3-y][Sr.sub.y]Mn[O.sub.3] are analyzed. The ferromagnetic ordering temperature [T.sub.c] has increased abruptly due to the increase in the competition between A-site size-disorder degree and double-exchange interaction resulting from Mn-O-Mn bond angle and the phase transition is broadened due to the cation disordering at A-site.

The effects of cation disorder and strain on the surface morphologies and transport properties of thin films with different A-site cation disorder, which is achieved by Y and Sr codoping into [La.sub.2/3][Ca.sub.1/3]Mn[O.sub.3], are examined. The spin-glass state and ferromagnetic-metallic state have coexisted in low temperature and cation disorder has induced more insulator phases in the large strain films.

The impact of the A-site disorder on low temperature dielectric and ferroelectric (FE) properties of SrTi[O.sub.3] is examined, with constant averaged A-site ionic size but different A-site cation size mismatching through the codoping of Ca and Ba. The studies have disclosed the transition from the quantum paraelectric state to relaxorlike ferroelectric state and eventually to normal ferroelectric state upon the increasing A-site disorder degree.

Abstract: SrTiO3−x thin films with various oxygen vacancies were fabricated by laser molecular beam epitaxy. The out-of-plane and in-plane lattice constants of the films increase with increasing oxygen vacancies, which was attributed to the increase of Ti3+ ions in the films. Ti3+ ions are formed only in the film inner which is revealed from X-ray photoemission spectroscopy (XPS). With varying the oxygen content, a metal-to-semiconductor transition was observed. The oxygen contents in the films, determined from lattice parameters and XPS are very consistent with each other, which shows quasi-quantitative methods to measure oxygen content in thin films. [Copyright &y& Elsevier]

Abstract: Modulation-doped Al0.22Ga0.78N/GaN heterostructure with 1000Å Si-doped n-Al0.22Ga0.78N barrier (n-AlGaN) were deposited on (0001)-oriented sapphire (α-Al2O3) by means of atmosphere-pressure metal-organic chemical vapor deposition. The reciprocal space mappings of symmetric reflection (0002) and asymmetric reflection (10 4) were measured with high resolution X-ray diffraction. The results indicate that the microstructure and strain status of barrier correlate to that of the underlying i-GaN layer. The barrier holds an “abnormal” strain-relaxation status, which probably results from the internal defects of n-AlGaN and the strain relaxation status at the i-GaN/α-Al2O3 interfaces. The results from grazing incidence X-ray diffraction show that the strain in barrier is nonuniform, which is consistent with the results from the reciprocal space mappings. [Copyright &y& Elsevier]

Abstract: Cations of Y and Sr co-substituting for La and Ca at A site in La2/3Ca1/3MnO3 compound, La2/3−x Y x Ca1/3−y Sr y MnO3, were synthesized successfully by solid-state reaction. X-ray diffraction shows there is only one phase with the dopants of Y and Sr within x ≤0.20 or y ≤0.19. The lattice parameters along a-, b-, and c-direction remain almost unchanged with x ≤0.20. The bond angle of Mnh name="sbnd" />Mn increases from 151.9° for x =0 to 172.7° for x =0.20 monotonically, which indicates that the Jahn–Teller effect in MnO6 octahedron decreases with increasing x. The temperature dependence of resistance with/without magnetic applied were measured and fitted theoretically. The metal-to-insulator transition temperature, T MI, decreases with increasing the Y content with x ≤0.10 while T MI increases slightly with further increasing x. The Y-content dependence of magnetoresistance shows a parabolic behavior. The maximum MR value corresponds to x =0.08–0.10. We attributed these variations in the structure and transportation to the cation disorder due to the cation doping. [Copyright &y& Elsevier]

We have synthesized the La doped YBa2−xLaxCu3Oy ceramic cuprates with x⩽0.30 by the solid state reaction technique under the quenching temperature from 350 to 650 °C. X-ray diffraction and scanning electron microscopy studies indicate that all the synthesized samples contain one single phase. La is replacing for Ba at Ba-site in YBa2Cu3Oy. The unit cell volume varies with La content and with the quenching temperature. The thermal expansion for the unit cell volume at different quenching temperature is discussed. For the full oxidation samples the zero resistance temperature, Tc0, is almost unchanged with x⩽0.20 whilst Tc0 decreases with the increase of La content for the quenched samples. The spin gap opening temperature, Ts, for all the quenched and annealing samples are determined from the temperature dependence of resistance. [Copyright &y& Elsevier]