We present X-ray diffraction and Raman spectroscopy investigations of (InxGa1–x)2O3 thin films and bulk-like ceramics in dependence of their composition. The thin films grown by pulsed laser deposition have a continuous lateral composition spread allowing the determination of phonon mode properties and lattice parameters with high sensitivity to the composition from a single 2-in. wafer. In the regime of low indium concentration, the phonon energies depend linearly on the composition and show a good agreement between both sample types. We determined the slopes of these dependencies for eight different Raman modes. While the lattice parameters of the ceramics follow Vegard's rule, deviations are observed for the thin films. Further, we found indications of the high-pressure phase InGaO3 II in the thin films above a critical indium concentration, its value depending on the type of substrate.

Iridate thin films are a prerequisite for any application utilizing their cooperative effects resulting from the interplay of strong spin-orbit coupling and electronic correlations. Here, heteroepitaxial Na 2 IrO 3 thin films with (001) out-of-plane crystalline orientation and well-defined in-plane epitaxial relationship are presented on various oxide substrates. Resistivity is dominated by a three-dimensional variable-range hopping mechanism in a large temperature range between 300 K and 40 K. Optical experiments show the onset of a small optical gap E go ≈ 200 meV and a splitting of the Ir 5d-t 2g manifold. Positive magnetoresistance below 3 T and 25 K shows signatures of a weak antilocalization effect.Transition-metal oxides containing 5d iridium ions allow for the observation of novel cooperative effects resulting from an interplay between strong spin-orbit coupling and electronic correlations. These iridates are promising candidates for high-T C superconductors, 1 spin liquids, 2-4 a novel J eff = 1/2 Mottinsulating ground state, 5,6 and topological insulators. 7-10 A rather recently studied iridate is the Mott-insulating layered compound Na 2 IrO 3 where edge-sharing IrO 6 octahedra form a honeycomb lattice within each Na 2 IrO 3 layer. 11 Theoretical studies of magnetic interactions in model Hamiltonians of A 2 BO 3 -type compounds 12,13 suggest spin liquid behavior in Na 2 IrO 3 . On the other hand, tight-binding model analyses and first-principles band structure calculations, 7,10,14 as well as density-matrix renormalization group calculations, 15 suggest Na 2 IrO 3 as a possible topological insulator. Both states of matter, however, promise possible application in fault-tolerant quantum computation. [16][17][18] Experimental efforts on Na 2 IrO 3 were so far limited to powder and single-crystalline samples. 11,19-22 Initially, from x-ray diffraction experiments a monoclinic C2/c unit cell for Na 2 IrO 3 was suggested. 11 More recent experiments however are more consistent with a C2/m unit cell. 19,20 Later experiments also confirm the presence of trigonal distortions of the IrO 6 octahedra and that structural disorder, i.e., stacking faults and Na/Ir site mixings, is common. The compound furthermore exhibits frustrated antiferromagnetic order below T N = 15 K with moments ordered collinearly in a zigzag pattern. 19-21 Furthermore, single-crystalline Na 2 IrO 3 has a small band gap. 22 Its temperature-dependent in-plane dc electrical resistivity follows a ρ ∝ exp[(T 0 /T ) 1/4 ] behavior between 100 and 300 K. 11 Such a ρ(T ) dependence is usually associated with three-dimensional Mott variable range hopping 23 of localized carriers.In this paper, we report on heteroepitaxial Na 2 IrO 3 thin films grown on (001) YAlO 3 , a-sapphire, and c-sapphire. Deposition of Na 2 IrO 3 thin films ultimately is a step towards future device applications of this material. Our heteroepitaxial films exhibit a clear epitaxial relation and an excellent (001) out-of-plane orientation. In magnetoresistance measurements we obs...

We present X-ray diffraction and Raman spectroscopy investigations of a (100)-oriented (AlxGa1–x)2O3 thin film on MgO (100) and bulk-like ceramics in dependence on their composition. The thin film grown by pulsed laser deposition has a continuous lateral composition spread allowing to determine precisely the dependence of the phonon mode properties and lattice parameters on the chemical composition. For x < 0.4, we observe the single-phase β-modification. Its lattice parameters and phonon energies depend linearly on the composition. We determined the slopes of these dependencies for the individual lattice parameters and for nine Raman lines, respectively. While the lattice parameters of the ceramics follow Vegard's rule, deviations are observed for the thin film. This deviation has only a small effect on the phonon energies, which show a reasonably good agreement between thin film and ceramics.

DC current induced metal-insulator transition in epitaxial Sm0.6Nd0.4NiO3/LaAlO3 thin film AIP Advances 4, 057102 (2014); 10.1063/1.4874642 Ruddlesden-Popper faults in LaNiO3/LaAlO3 superlattices Effect of charge modulation in ( La V O 3 ) m ( Sr V O 3 ) n superlattices on the insulator-metal transition

97 39286LaNiO 3 (LNO) thin films were grown using pulsed laser deposition. The c-axis, i.e., out-of-plane lattice parameter of the films was controlled reproducibly by using different substrate materials and by variation of oxygen partial pressure and growth temperature. The out-of-plane (c-axis) strain of LNO deposited on LaAlO 3 with increasing oxygen pressure changed from positive to negative. All the films show an excellent metallic conductivity with positive resistivity temperature coefficient. Lowest resistivity was about 300 mV cm. At high and low temperatures, the resistivity is explained by electron-phonon scattering and electron-electron interaction, respectively. In addition, the resistivity shows a clear dependence on the c-axis strain of LNO films. With increasing strain, the resistivity increases. However, this effect is much more pronounced for negative c-axis strain.Strain-dependent resistivity of LNO films on LAO at the indicated measurement temperatures. The inset is a typical AFM image of the LNO film surface.1 Introduction The conduction band of perovskite nickelates (RNiO 3 , where R ¼ rare earth) is formed by the overlap of the Ni 3d orbitals and the O 2p orbitals. Most perovskite nickelates exhibit a temperature-driven metal-toinsulator transition [1,2], which is related to the strongly distorted perovskite structure and the size of the rare-earth ion R [3, 4]. However, LaNiO 3 (LNO) is the only member that remains metallic down to the lowest temperatures [5]. For this reason, LNO is an excellent candidate for use as an electrode in oxide electronics, in particular at low temperature. The primitive cell of bulk LNO is rhombohedral with angle a ¼ 60.498. It is reasonably well approximated by a pseudocubic cell with a ¼ 0.3838 nm. Several efforts have been undertaken to prepare LNO thin films by sputtering [6], pulsed laser deposition (PLD) [7], molecular beam