A systematic study on the site occupancy of rare-earth cations in Ba-rich and Ti-rich BaTiO3 fired in reducing atmosphere is performed. The corresponding lattice relaxation is used as an indicator of site occupancy and, to a lesser extent, defect structures. Accurate lattice parameters are obtained from X-ray diffraction data that is analyzed with the maximum likelihood method to account for correlated errors in the c and a lattice parameters. Comparisons of lattice volume as a function of ionic radius of the dopant reveals three regimes, with the intermediate sized cations (0.087 nm \leqslantr \leqslant0.094 nm where r is the ionic radius in six-fold coordination) demonstrating amphoteric behavior (occupying A- or B-sites). Defect chemistry analysis of site occupancy links the importance of metal vacancy ratios and oxygen vacancy concentrations with site occupancy. The trends predicted from the defect chemistry analysis are consistent with the observed lattice relaxations.

We report the growth, epitaxial arrangement, and electrical and magnetic properties of epitaxial thin films of hexagonal BaRuO 3 on ͑001͒ cubic perovskite substrates. Four-circle x-ray diffraction reveals that the BaRuO 3 films are predominantly grown with two distinct orientations normal to the ͑001͒ SrTiO 3 substrate: (022 3) of the four-layered hexagonal structure ͑4H͒ in the sputter-grown films and (202 5) of the nine-layered hexagonal structure ͑9R͒ in the pulsed laser deposited films. (022 3)-oriented 4H films consist of four orthogonal domains with the in-plane relationship of BaRuO 3 ͓21 1 0͔//SrTiO 3 ͗110͘. The temperature dependent resistivity of the (022 3) 4H film shows metallic behavior. In contrast, a resistivity minimum is observed at low temperatures in the (202 5 3 The striking difference between SrRuO 3 and CaRuO 3 in magnetic properties makes BaRuO 3 interesting, particularly if BaRuO 3 also has a pseudocubic perovskite structure. Bulk BaRuO 3 ceramics have been synthesized with three different crystal structures as a function of synthesis pressure. 4 As the synthesis pressure increases, BaRuO 3 transforms to the structure containing more cubicclose packing and fewer hexagonal-close packing of BaO 3 layers; from the nine-layered rhombohedral ͑9R͒ with a ϭ5.75 Å and cϭ21.6 Å, 4,5 to the four-layered hexagonal ͑4H͒ with aϭ5.73 Å and cϭ9.5 Å, 4,6 and finally the sixlayered hexagonal ͑6H͒ with aϭ5.71 Å and cϭ14 Å.4 Much higher pressures ͑about 125 kbars͒ are expected to be necessary to form the pseudocubic polymorph of BaRuO 3 , with an extrapolated lattice constant of 4.01 Å. 4,7 It is also possible that one might be able to stabilize the pseudocubic phase by epitaxial growth using cubic perovskite substrates.Despite our efforts to grow the desired perovskite structure, both the pulsed laser deposited ͑PLD͒ films and the sputter-grown films were not the perovskite phase, and we were unsuccessful in growing pseudocubic BaRuO 3 on ͑001͒ cubic perovskite substrates.7 This is in contrast to a prior report 8 on the synthesis of tetragonal BaRuO 3 thin films on (001) SrTiO 3 using rf sputtering techniques. However, the structural evidence presented by Fukushima et al. 8 is insufficient to establish whether their films are indeed the tetragonal polymorph of BaRuO 3 or are instead the 4H or 9R polymorph. 7In this letter we report the growth of epitaxial thin films of hexagonal BaRuO 3 on ͑001͒ cubic perovskite substrates. We show that films containing predominantly a metastable 4H structure 4,6 ͓and a minor amount of (202 5) 9R BaRuO 3 ] can be grown along a high index orientation, (022 3), by the 90°off-axis sputtering technique. A previous study 7 has also shown that PLD grown films are mixed with (202 5) 9R and (022 3) 4H BaRuO 3 on the same ͑001͒ substrate. Here the electrical transport and magnetic properties of both the predominantly (022 3) 4H and (202 5) 9R films are discussed.The films were grown on the cubic face of a variety of substrates, which include (001) LaAlO 3 (aϭ3.792 Å), (001) SrTiO 3...

No abstract