18 research outputs found
Thermal Expansion in BaRuO3 Perovskites ā 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 Ā°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 Ā°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 perovskitesāan 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 Ā°C using high resolution synchrotron X-ray diffraction. The structural studies reveal a systematic decrease of the RuāRu distance as the pressure required to prepare the polytype increases. The OāO distance across the shared face increases as the RuāRu separation decreases. The 9R and 4H polytypes undergo unexceptional changes with increasing temperature. In 6H-BaRuO3 there is an apparent increase in the RuāRu interaction at around 650 Ā°C and a concurrent reduction in the OāO distance, indicating an anomalous strengthening of the RuāRu interactions upon heating.Depto. de QuĆmica InorgĆ”nicaFac. de Ciencias QuĆmicasTRUEpu
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 ā¼90 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. Ā© 2009 American Chemical Society
High-Pressure Synthesis, Crystal Structure, and Phase Stability Relations of a LiNbO<sub>3</sub>āType Polar Titanate ZnTiO<sub>3</sub> and Its Reinforced Polarity by the Second-Order JahnāTeller Effect
A polar
LiNbO<sub>3</sub>-type (LN-type) titanate ZnTiO<sub>3</sub> has been
successfully synthesized using ilmenite-type (IL-type)
ZnTiO<sub>3</sub> under high pressure and high temperature. The first
principles calculation indicates that LN-type ZnTiO<sub>3</sub> 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 ZnTiO<sub>3</sub> crystallizes into a hexagonal structure with a polar space group <i>R</i>3<i>c</i> and exhibits greater intradistortion
of the TiO<sub>6</sub> octahedron in LN-type ZnTiO<sub>3</sub> than
that of the SnO<sub>6</sub> octahedron in LN-type ZnSnO<sub>3</sub>. The estimated spontaneous polarization (75 Ī¼C/cm<sup>2</sup>, 88 Ī¼C/cm<sup>2</sup>) using the nominal charge and the Born
effective charge (BEC) derived from density functional perturbation
theory, respectively, are greater than those of ZnSnO<sub>3</sub> (59
Ī¼C/cm<sup>2</sup>, 65 Ī¼C/cm<sup>2</sup>), 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 ZnTiO<sub>3</sub> is greater than that of
LiNbO<sub>3</sub> (62 Ī¼C/cm<sup>2</sup>, 76 Ī¼C/cm<sup>2</sup>), indicating that LN-type ZnTiO<sub>3</sub>, like LiNbO<sub>3</sub>, is a candidate ferroelectric material with high performance.
The second harmonic generation (SHG) response of LN-type ZnTiO<sub>3</sub> is 24 times greater than that of LN-type ZnSnO<sub>3</sub>. The findings indicate that the intraoctahedral distortion, spontaneous
polarization, and the accompanying SHG response are caused by the
stabilization of the polar LiNbO<sub>3</sub>-type structure and reinforced
by the second-order JahnāTeller effect attributable to the
orbital interaction between oxygen ions and d<sup>0</sup> ions such
as Ti<sup>4+</sup>
High-Pressure Synthesis of <i>A</i>āSite Ordered Double Perovskite CaMnTi<sub>2</sub>O<sub>6</sub> and Ferroelectricity Driven by Coupling of <i>A</i>āSite Ordering and the Second-Order JahnāTeller Effect
We successfully synthesized a novel
ferroelectric <i>A</i>-site-ordered double perovskite CaMnTi<sub>2</sub>O<sub>6</sub> 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 SiO<sub>2</sub> (Ī±-quartz). This compound
possesses a tetragonal polar structure with space group <i>P</i>4<sub>2</sub><i>mc</i>. <i>P</i>-<i>E</i> hysteresis measurement demonstrated that CaMnTi<sub>2</sub>O<sub>6</sub> is also ferroelectric. A spontaneous polarization calculated
by use of point charge model and the observed remnant polarization
are 24 and 3.5 Ī¼C/cm<sup>2</sup>, respectively. CaMnTi<sub>2</sub>O<sub>6</sub> undergoes a ferroelectricāparaelectric orderādisorder-type
phase transition at 630 K. The structural analysis implies that both
the ordering of shift of Mn<sup>2+</sup> from the square-planar and
the off-center displacement of Ti<sup>4+</sup> in TiO<sub>6</sub> octahedra
are responsible for ferroelectricity. CaMnTi<sub>2</sub>O<sub>6</sub> belongs to a new class of ferroelectrics in which <i>A</i>-site ordering and second-order JahnāTeller distortion are
cooperatively coupled. The finding gave us a new concept for the design
of ferroelectric materials