Thermal Expansion in BaRuO3 Perovskites – an unusual case of bond strengthening at high temperatures

The temperature dependence of the structures of three polytypes of BaRuO3 have been investigated between room temperature and 1000 °C using high resolution Synchrotron X-ray diffraction. The structural studies reveal a systematic decrease in the Ru-Ru distance as the pressure required to prepare the polytype increases. The O-O distance across the shared face increases as the Ru-Ru separation decreases. The 9R and 4H polytypes undergo unexceptional changes with increasing temperature. In 6H-BaRuO3 there is an apparent increase in the Ru-Ru interaction around 650 °C and concurrent reduction in the O-O distance indicating an anomalous strengthening of the Ru-Ru interactions upon heating.Australian Synchrotron Australian Research Counci

Superconductivity suppression of Ba0.5K0.5Fe2-2xM2xAs2 single crystals by substitution of transition-metal (M = Mn, Ru, Co, Ni, Cu, and Zn)

We investigated the doping effects of magnetic and nonmagnetic impurities on the single-crystalline p-type Ba0.5K0.5Fe2-2xM2xAs2 (M = Mn, Ru, Co, Ni, Cu and Zn) superconductors. The superconductivity indicates robustly against impurity of Ru, while weakly against the impurities of Mn, Co, Ni, Cu, and Zn. However, the present Tc suppression rate of both magnetic and nonmagnetic impurities remains much lower than what was expected for the s\pm-wave model. The temperature dependence of resistivity data is observed an obvious low-T upturn for the crystals doped with high-level impurity, which is due to the occurrence of localization. Thus, the relatively weak Tc suppression effect from Mn, Co, Ni, Cu, and Zn are considered as a result of localization rather than pair-breaking effect in s\pm-wave model.Comment: 8 pages, 9 figures, to be published in Phys. Rev.

Ba2NiOsO6: A Dirac-Mott insulator with ferromagnetism near 100 K

The ferromagnetic semiconductor Ba2NiOsO6 (Tmag ~100 K) was synthesized at 6 GPa and 1500 {\deg}C. It crystallizes into a double perovskite structure [Fm-3m; a = 8.0428(1) {\AA}], where the Ni2+ and Os6+ ions are perfectly ordered at the perovskite B-site. We show that the spin-orbit coupling of Os6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (Tmag < 180 K), the spin-gapless semiconductor Mn2CoAl (Tmag ~720 K), and the ferromagnetic insulators EuO (Tmag ~70 K) and Bi3Cr3O11 (Tmag ~220 K). It is also qualitatively different from known ferrimagnetic insulator/semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba2NiOsO6 should increase interest in the platinum group oxides, because this new class of materials should be useful in the development of spintronic, quantum magnetic, and related devices

Thermal expansion in BaRuO3 perovskites–an unusual case of bond strengthening at high temperatures

The temperature dependences of the structures of three polytypes of BaRuO3 have been investigated between room temperature and 1000 °C using high resolution synchrotron X-ray diffraction. The structural studies reveal a systematic decrease of the Ru–Ru distance as the pressure required to prepare the polytype increases. The O–O distance across the shared face increases as the Ru–Ru separation decreases. The 9R and 4H polytypes undergo unexceptional changes with increasing temperature. In 6H-BaRuO3 there is an apparent increase in the Ru–Ru interaction at around 650 °C and a concurrent reduction in the O–O distance, indicating an anomalous strengthening of the Ru–Ru interactions upon heating.Depto. de Química InorgánicaFac. de Ciencias QuímicasTRUEpu

Synthesis and magnetic and charge-transport properties of the correlated 4d post-perovskite CaRhO 3

A high-quality polycrystalline sample of the correlated 4d post-perovskite CaRhO 3 (Rh 4+:4d 5, S e = 1/2) was attained under a moderate pressure of 6 GPa. Since the post-perovskite is quenchable at ambient pressure/temperature, it can be a valuable analogue of the post-perovskite MgSiO 3 (stable higher than 120 GPa and unstable at ambient pressure), which is a significant key material in earth science. The sample was subjected for measurements of charge-transport and magnetic properties. The data clearly indicate it goes into an antiferromagnetically ordered state below ∼90 K in an unusual way, in striking contrast to what was observed for the perovskite phase. The post-perovskite CaRhO 3 offers future opportunities for correlated electrons science as well as earth science. © 2009 American Chemical Society

High-Pressure Synthesis, Crystal Structure, and Phase Stability Relations of a LiNbO₃‑Type Polar Titanate ZnTiO₃ and Its Reinforced Polarity by the Second-Order Jahn–Teller Effect

A polar LiNbO₃-type (LN-type) titanate ZnTiO₃ has been successfully synthesized using ilmenite-type (IL-type) ZnTiO₃ under high pressure and high temperature. The first principles calculation indicates that LN-type ZnTiO₃ is a metastable phase obtained by the transformation in the decompression process from the perovskite-type phase, which is stable at high pressure and high temperature. The Rietveld structural refinement using synchrotron powder X-ray diffraction data reveals that LN-type ZnTiO₃ crystallizes into a hexagonal structure with a polar space group <i>R</i>3<i>c</i> and exhibits greater intradistortion of the TiO₆ octahedron in LN-type ZnTiO₃ than that of the SnO₆ octahedron in LN-type ZnSnO₃. The estimated spontaneous polarization (75 μC/cm², 88 μC/cm²) using the nominal charge and the Born effective charge (BEC) derived from density functional perturbation theory, respectively, are greater than those of ZnSnO₃ (59 μC/cm², 65 μC/cm²), which is strongly attributed to the great displacement of Ti from the centrosymmetric position along the <i>c</i>-axis and the fact that the BEC of Ti (+6.1) is greater than that of Sn (+4.1). Furthermore, the spontaneous polarization of LN-type ZnTiO₃ is greater than that of LiNbO₃ (62 μC/cm², 76 μC/cm²), indicating that LN-type ZnTiO₃, like LiNbO₃, is a candidate ferroelectric material with high performance. The second harmonic generation (SHG) response of LN-type ZnTiO₃ is 24 times greater than that of LN-type ZnSnO₃. The findings indicate that the intraoctahedral distortion, spontaneous polarization, and the accompanying SHG response are caused by the stabilization of the polar LiNbO₃-type structure and reinforced by the second-order Jahn–Teller effect attributable to the orbital interaction between oxygen ions and d⁰ ions such as Ti⁴⁺

High-Pressure Synthesis of <i>A</i>‑Site Ordered Double Perovskite CaMnTi₂O₆ and Ferroelectricity Driven by Coupling of <i>A</i>‑Site Ordering and the Second-Order Jahn–Teller Effect

We successfully synthesized a novel ferroelectric <i>A</i>-site-ordered double perovskite CaMnTi₂O₆ under high-pressure and investigated its structure, ferroelectric, magnetic and dielectric properties, and high-temperature phase transition behavior. Optical second harmonic generation signal, by frequency doubling 1064 nm radiation to 532 nm, was observed and its efficiency is about 9 times as much as that of SiO₂ (α-quartz). This compound possesses a tetragonal polar structure with space group <i>P</i>4₂<i>mc</i>. <i>P</i>-<i>E</i> hysteresis measurement demonstrated that CaMnTi₂O₆ is also ferroelectric. A spontaneous polarization calculated by use of point charge model and the observed remnant polarization are 24 and 3.5 μC/cm², respectively. CaMnTi₂O₆ undergoes a ferroelectric–paraelectric order–disorder-type phase transition at 630 K. The structural analysis implies that both the ordering of shift of Mn²⁺ from the square-planar and the off-center displacement of Ti⁴⁺ in TiO₆ octahedra are responsible for ferroelectricity. CaMnTi₂O₆ belongs to a new class of ferroelectrics in which <i>A</i>-site ordering and second-order Jahn–Teller distortion are cooperatively coupled. The finding gave us a new concept for the design of ferroelectric materials