The lattice parameters of three perovskite-related oxides have been measured with high precision at room temperature. An accuracy of the order of 10(-5) has been achieved by applying a sophisticated high-resolution X-ray diffraction technique which is based on the modified Bond method. The results on cubic SrTiO(3) [a = 3.905268 (98) Å], orthorhombic DyScO(3) [a = 5.442417 (54), b = 5.719357 (52) and c = 7.904326 (98) Å], and orthorhombic NdGaO(3) [a = 5.428410 (54), b = 5.498407 (55) and c = 7.708878 (95) Å] are discussed in view of possible systematic errors as well as non-stoichiometry in the crystals.

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Homoepitaxial (100) β-Ga2O3 films were grown on substrates with miscut angles of 2°, 4°, and 6° toward [001¯] by metal organic vapor phase epitaxy. Step-flow growth mode, resulting in smooth film surfaces and high crystalline quality, could only be achieved if the diffusion length on the film surface corresponds approximately to the width of the terraces. Otherwise, 2D islands or step-bunching is obtained, which results in a deteriorated crystalline quality and reduced Hall mobility of the electrons. By varying the growth parameters such as the O2/Ga ratio, Ar push gas flow, and chamber pressure, the diffusion length could be adjusted so that step-flow growth mode could be achieved at all miscut angles. Furthermore, the growth rate could remarkably be increased from 1.6 nm/min to 4.3 nm/min. For homoepitaxial β-Ga2O3 films grown in step-flow growth mode, TEM measurements revealed a high crystalline quality, which is correlated with a high Hall mobility of 131 cm2/V s at a carrier concentration of 1.6 × 1017cm−3, which is comparable with β-Ga2O3 single crystal bulk values. This study clearly points out the high potential of β-Ga2O3 films for high performance MOSFETs if the influence of the deposition parameters on the structural and electrical properties is well understood.

Epitaxially strained NaNbO 3 films were grown by liquid-delivery spin metalorganic chemical vapour deposition on several oxide substrates, inducing tensile and compressive lattice strain. High-resolution X-ray diffraction measurements reveal that coherently grown compressively strained NaNbO 3 films on NdGaO 3 exhibit the orthorhombic c phase. With increasing in-plane strain a first structural phase transition to the monoclinic r phase and, further on, for films grown under tensile strain on rare earth scandates, a second phase transition to the aa phase, are observed. Our results are in good agreement with the pathway of phase transitions predicted by Dié guez, Rabe & Vanderbilt [Phys. Rev. B, (2005), 72, 144101] for NaNbO 3 films.

A novel concept to obtain a ferroelectric material with enhanced piezoelectric properties is proposed. This approach is based on the combination of two pathways: (i) the evolution of a ferroelectric monoclinic phase and, (ii) the coexistence of different types of ferroelectric domains leading to polarization discontinuities at the domain walls. Each of these pathways enables polarization rotation in the material which is responsible for giant piezoelectricity. Targeted incorporation of anisotropic epitaxial lattice strain is used to implement this approach. The feasibility of our concept is demonstrated for KNaNbO epitaxial layers grown on NdScO substrates where the coexistence of (100) and (001) pseudocubic oriented monoclinic domains is experimentally verified. This coexistence results in a complex periodic domain pattern with alternating emergence of ferroelectric in-plane a a and inclined M monoclinic phases, which differ in the direction of the electrical polarization vector. Our approach opens the possibility to exploit ferroelectric properties in both vertical and lateral directions and to achieve enhanced piezoelectric properties in lead-free material caused by singularities at the domains walls.