Search

A-site columnar-ordered double perovskites, LnMn(Ga0.5Ti0.5)2O6 (Ln = Sm, Gd), were successfully synthesized under high pressure and high temperature (6 GPa, 1375 K). From the synchrotron powder X-ray diffraction patterns, all of the diffraction peaks can be indexed by the P42/nmc space group with lattice parameters a, c ≈ 2ap (ap: primitive cubic perovskite lattice) and no ordering of the B-site cations. Rietveld analysis of the synchrotron powder X-ray diffraction patterns and Curie–Weiss fitting of their magnetizations reveal that the ionic formulae of these perovskites are Ln3+Mn2+(Ga3+0.5Ti4+0.5)2O2–6. SmMn(Ga0.5Ti0.5)2O6 shows canted-antiferromagnetic behavior, whereas GdMn(Ga0.5Ti0.5)2O6 exhibits two different magnetic states at low temperature depending on the applied magnetic field and shows an unusual magnetization curve. These magnetic behaviors originate by decreasing the antiferromagnetic interaction by substituting Ga3+(d10) for Ti4+(d0) and by decreasing the ferromagnetic interaction between columnar-ordered Ln3+ and Mn2+.

The synthesis of multicomponent perovskites (Ln0.25Mn0.75)(Al0.25Ti0.75)O3 (Ln=La, Pr, Nd, Sm, Gd, Tb, Dy, Y) have been investigated using a high-pressure and high-temperature (6 GPa, 1175 °C) technique. When Ln3+ is larger La3+, Pr3+, Nd3+, the A-site ordered perovskites, LnMn3(Al0.25Ti0.75)4O12 in Im-3, have been successfully synthesized. The A-site partially disordered one, (Sm0.80Mn0.20)(Sm0.07Mn0.93)3(Al0.25Ti0.75)4O12 is also obtained. In the case of smaller Gd3+, Tb3+, Dy3+, we have obtained no single phase but two decomposed perovskite phases. When Ln3+ is much smaller Y3+, it is crystallized as an A-site disorder one in Pnma. The Rietveld structural refinements of the A-site ordered and partially disordered perovskites indicate that the tilting of (Al/Ti)O6 octahedrons for the A-site ions ordering is correlated with the (Al/Ti)–O and Ln–O bond lengths to optimize the coordination of the A- and A′-sites. The phase stability of the A-site ordered perovskites is discussed from the viewpoint of this correlation.

A new multicomponent A-site ordered perovskite-type oxide has been successfully synthesized in the BiFeO 3 and MnTiO 3 pseudobinary system at high pressure and temperature, 6 GPa and 1300 K. It is found that the oxide is an A-site ordered and B-site disordered perovskite Bi 3+ Mn 2+ 3 (Fe 3+ 0.25 Ti 4+ 0.75 ) 4 O 12 in the space group of the cubic high symmetry Im -3 with a lattice parameter a =7.5937(3) A. It should be noted that the Mn 2+ ions in the A ′-site show a site-splitting, while the Bi 3+ ones are in a regular icosahedron position of the A -site. On the other hand, the Fe 3+ and Ti 4+ ones in the B -site are disordered in this perovskite structure. The temperature dependence of magnetizations and specific heats at low temperatures shows spin-glass-like behaviors below 11 K.

The temperature dependences of the structures of three polytypes of BaRuO

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 Council

We successfully synthesized a novel ferroelectric A-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 P42mc. P-E 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 bel...

Phase transitions in NaZnF 3 and NaMnF 3 were examined up to 24 GPa and 1100 °C using a multianvil apparatus. NaZnF 3 perovskite transforms to postperovskite above 11–16 GPa at 600–1000 °C, and the postperovskite is quenchable at ambient conditions. The NaZnF 3 perovskite–postperovskite transition boundary is expressed as P (GPa) = 4.9 + 0.011 T (°C). At 8–11 GPa and 900–1100 °C, NaMnF 3 perovskite dissociates into two phases of Na 3 Mn 2 F 7 and MnF 2 . The latter phase is suggested to have the structure of orthorhombic-I type ZrO 2 or cotunnite. Using available experimental data on the perovskite–postperovskite transitions in thirteen compounds of A 2+ B 4+ O 3 and A + B 2+ F 3 , several crystal-chemical characteristics of the transition are elucidated as follows. In the transition, the volume change is between −1% and −2%, and the Clapeyron slope of the boundary is 10–17 MPa/°C. These support reliability of recently determined Clapeyron slope of 13 MPa/°C in MgSiO 3 which suggests that the perovskite–postperovskite boundary intersects the temperature profile twice in the D″ layer. Postperovskites of ABX 3 whose enthalpies are higher by more than 70 kJ/mol relative to the phase stable at 1 atm are unquenchable, while those by less than 15 kJ/mol are quenchable to ambient conditions. Structure refinements indicate that A + B 2+ F 3 postperovskites quenched at 1 atm are more similar to that of MgSiO 3 postperovskite at high pressure, than those of quenched A 2+ B 4+ O 3 postperovskites. With increasing pressure, octahedral tilt angles of both A 2+ B 4+ O 3 and A + B 2+ F 3 perovskites increase, resulting in transition to postperovskite at the angle of about 26°, and fluoride perovskites are more rapidly distorted with pressure than oxide perovskites. Covalent character of B–X bonds of ABX 3 postperovskite is suggested to be favorable for stabilization of the postperovskite structure. All these features suggest that NaNiF 3 is a good quenchable, low-pressure analogue compound to MgSiO 3 to investigate the perovskite–postperovskite transition.

The ferromagnetic semiconductor $\mathrm{B}{\mathrm{a}}_{2}\mathrm{NiOs}{\mathrm{O}}_{6}$ (${T}_{\mathrm{mag}}\ensuremath{\sim}100\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) was synthesized at 6 GPa and 1500 \ifmmode^\circ\else\textdegree\fi{}C. It crystallizes into a double perovskite structure [$Fm\ensuremath{-}3m$; $a=8.0428(1)\phantom{\rule{0.16em}{0ex}}\AA{}$], where the $\mathrm{N}{\mathrm{i}}^{2+}$ and $\mathrm{O}{\mathrm{s}}^{6+}$ ions are perfectly ordered at the perovskite $B$ site. We show that the spin-orbit coupling of $\mathrm{O}{\mathrm{s}}^{6+}$ 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 $g21\phantom{\rule{0.16em}{0ex}}\mathrm{kOe}$ 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 (${T}_{\mathrm{mag}}l180\phantom{\rule{0.16em}{0ex}}\mathrm{K}$), the spin-gapless semiconductor $\mathrm{M}{\mathrm{n}}_{2}\mathrm{CoAl}$ (${T}_{\mathrm{mag}}\ensuremath{\sim}720\phantom{\rule{0.16em}{0ex}}\mathrm{K}$), and the ferromagnetic insulators EuO (${T}_{\mathrm{mag}}\ensuremath{\sim}70\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) and $\mathrm{B}{\mathrm{i}}_{3}\mathrm{C}{\mathrm{r}}_{3}{\mathrm{O}}_{11}$ (${T}_{\mathrm{mag}}\ensuremath{\sim}220\phantom{\rule{0.16em}{0ex}}\mathrm{K}$). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of $\mathrm{B}{\mathrm{a}}_{2}\mathrm{NiOs}{\mathrm{O}}_{6}$ should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.

Polycrystals of Ba0.5K0.5Fe1.9M0.1As2 (M = Fe, Co, Ni, Cu, and Zn) synthesized at high pressures show quasi-periodic spikes in the magnetization loop at 2 K owing to successive flux jumps, while the single crystals are observed as absence of jumps. The Zn-doped crystal indicates higher frequency flux jumps than that of Zn-free samples, because of the reduction of grain size and enhancement of grain boundary effect. However, the Co-, Ni- and Cu-doped crystals show less jumps duo to the increased granularity. Our present results suggest that the flux jump in the textured polycrystals is controlled largely by the grain boundary as the flux pining effect rather than the intrinsic dopants.

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 R3c 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/cm(2), 88 μC/cm(2)) 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/cm(2), 65 μC/cm(2)), which is strongly attributed to the great displacement of Ti from the centrosymmetric position along the c-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/cm(2), 76 μC/cm(2)), 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 d(0) ions such as Ti(4+).

Metals cannot exhibit ferroelectricity because static internal electric fields are screened by conduction electrons, but in 1965, Anderson and Blount predicted the possibility of a ferroelectric metal, in which a ferroelectric-like structural transition occurs in the metallic state. Up to now, no clear example of such a material has been identified. Here we report on a centrosymmetric (R-3c) to non-centrosymmetric (R3c) transition in metallic LiOsO3 that is structurally equivalent to the ferroelectric transition of LiNbO3. The transition involves a continuous shift in the mean position of Li+ ions on cooling below 140K. Its discovery realizes the scenario described by Anderson and Blount, and establishes a new class of materials whose properties may differ from those of normal metals., Manuscript of published version, including Supplementary Information. See also News & Views article by V. Keppens, Nature Materials 12, 952 (2013)

Correction for 'New layered cobalt oxyfluoride, Sr

A high-pressure phase of CaRhO3 stable between perovskite and post-perovskite in P-T space was synthesized at 17 GPa and 1650 °C using a multi-anvil apparatus. The crystal structure of CaRhO3 was solved by the structure prediction evolutionary algorithm and was refined by Rietveld analysis of the synchrotron powder X-ray diffraction pattern, along with transmission electron microscopy observations. The structure is monoclinic with lattice parameters of a = 12.5114(1) A, b = 3.1241(1) A, c = 8.8579(1) A, β = 103.951(1)°, V = 336.01(1) A 3 with space group P21/m. The structure contains edge-sharing RhO6 octahedral chains along the b-axis. The six RhO6 octahedral chains make a unit, which stacks up alternatively with the CaO8 polyhedral layer along the [101] direction to form the structure of CaRhO3 intermediate phase.

Topotactic reaction of the n = 2 Ruddlesden–Popper phase Sr3Fe2O7−δ (δ ≈ 0.18) with polytetrafluoroethylene (PTFE) yields a highly fluorinated phase Sr3Fe2O5+xF2–x (x ≈ 0.44), compared with Sr3Fe2O6F0.87 prepared by the reaction of Sr3Fe2O6 and F2 gas. Structure analyses based on powder neutron diffraction, synchrotron powder diffraction, and 57Fe Mossbauer spectroscopy measurements demonstrate that the new oxyfluoride perovskite has no anion deficiencies and adopts the tetragonal structure (space group I4/mmm) with the lattice constants a = 3.87264(6) A and c = 21.3465(6) A at room temperature. The fluoride ions preferentially occupy the terminal apical anion sites with oxide ions in a disordered manner, which results in square pyramidal coordination around iron. The present compound also shows an antiferromagnetic order with a Neel temperature (TN) of 390 K, in sharply contrast to Sr3Fe2O6F0.87, which has a TN value that is lower than room temperature.

Superconducting cubic δ-MoC0.75 has been synthesized by a high-pressure synthesis method at a pressure of 17 GPa in a Kawai-type instrument, followed by studies on the crystal structure by synchrotron X-ray diffraction. Electromagnetic measurements indicated a superconducting transition temperature Tc of 14.3 K, which is the highest Tc value experimentally confirmed among the binary metal carbides. The cubic δ-MoC0.75 prepared in this study could be considered as a weakly coupled superconductor.

The valence-band electronic structures of high-pressure-phase PdF2-type (HP-PdF2-type) platinum-group metal dioxides MO2 (M = Ru, Rh, Ir, and Pt) were studied by synchrotron radiation photoelectron spectroscopy and first-principles calculations. The obtained photoelectron spectra for HP-PdF2-type RuO2, RhO2, and IrO2 agree well with the calculated valence-band densities of states (DOSs) for these compounds, indicating their metallic properties, whereas the DOS of HP-PdF2-type PtO2 (calculated in the presence and absence of spin–orbit interactions) predicts that this material may be metallic or semimetallic, which is inconsistent with the electric conductivity reported to date and the charging effect observed in current photoelectron measurements. Compared with the calculated results, the valence-band spectrum of PtO2 appears to have shifted toward the high-binding-energy side and reveals a gradual intensity decrease toward the Fermi energy EF, implying a semiconductor-like electronic structure. Spin-depen...

High-pressure phase transitions of CaRhO3 perovskite were examined at pressures of 6–27 GPa and temperatures of 1,000–1,930°C, using a multi-anvil apparatus. The results indicate that CaRhO3 perovskite successively transforms to two new high-pressure phases with increasing pressure. Rietveld analysis of powder X-ray diffraction data indicated that, in the two new phases, the phase stable at higher pressure possesses the CaIrO3-type post-perovskite structure (space group Cmcm) with lattice parameters: a = 3.1013(1) A, b = 9.8555(2) A, c = 7.2643(1) A, V m = 33.43(1) cm3/mol. The Rietveld analysis also indicated that CaRhO3 perovskite has the GdFeO3-type structure (space group Pnma) with lattice parameters: a = 5.5631(1) A, b = 7.6308(1) A, c = 5.3267(1) A, V m = 34.04(1) cm3/mol. The third phase stable in the intermediate P, T conditions between perovskite and post-perovskite has monoclinic symmetry with the cell parameters: a = 12.490(3) A, b = 3.1233(3) A, c = 8.8630(7) A, β = 103.96(1)°, V m = 33.66(1) cm3/mol (Z = 6). Molar volume changes from perovskite to the intermediate phase and from the intermediate phase to post-perovskite are –1.1 and –0.7%, respectively. The equilibrium phase relations determined indicate that the boundary slopes are large positive values: 29 ± 2 MPa/K for the perovskite—intermediate phase transition and 62 ± 6 MPa/K for the intermediate phase—post-perovskite transition. The structural features of the CaRhO3 intermediate phase suggest that the phase has edge-sharing RhO6 octahedra and may have an intermediate structure between perovskite and post-perovskite.

High-pressure phase relations in CaRuO 3 were examined at 13–27 GPa and 900–1200 °C using a multi-anvil apparatus. At about 21–25 GPa at 900–1200 °C, CaRuO 3 with orthorhombic perovskite structure transformed to CaIrO 3 -type post-perovskite structure. The phase boundary of the post-perovskite transition in CaRuO 3 was determined as P (GPa) = 0.010 × T (°C) + 12.4. The post-perovskite phase of CaRuO 3 was quenchable to ambient conditions like that of CaIrO 3 . Rietveld refinement confirmed that CaRuO 3 post-perovskite and perovskite have the structures of CaIrO 3 -type post-perovskite (space group Cmcm ) and GdFeO 3 -type orthorhombic perovskite ( Pbnm ), respectively. Lattice parameters and unit cell volume of CaRuO 3 post-perovskite were determined to be a = 3.1150(1) A, b = 9.8268(1) A, c = 7.2963(1) A and V = 223.34(1) A 3 , and those of CaRuO 3 perovskite a = 5.3635(2) A, b = 5.5261(2) A, c = 7.6668(2) A and V = 227.24(1) A 3 . The structural features of CaRuO 3 post-perovskite and perovskite are similar to those of the polymorphs of CaIrO 3 and MgSiO 3 . The post-perovskite transition in CaRuO 3 is consistent with the general tendency that orthorhombic perovskites with relatively large tilting of the octahedral framework transform to post-perovskite structure at high pressure. CaRuO 3 would be a low-pressure, quenchable analogue material suitable for investigation on the post-perovskite phase transition of MgSiO 3 .

Polycrystalline high-pressure modifications of the PdF2-type MO2 (M: Ru, Rh, Os, Ir, Pt) are prepared from their rutile-type precursors and KClO4 as reduction inhibitor (Pt capsule in multianvil press, 17 GPa, 1273 K).

The perovskite PbCrO3 is an antiferromagnetic insulator. However, the fundamental interactions leading to the insulating state in this single-valent perovskite are unclear. Moreover, the origin of the unprecedented volume drop observed at a modest pressure of P = 1.6 GPa remains an outstanding problem. We report a variety of in situ pressure measurements including electron transport properties, X-ray absorption spectrum, and crystal structure study by X-ray and neutron diffraction. These studies reveal key information leading to the elucidation of the physics behind the insulating state and the pressure-induced transition. We argue that a charge disproportionation 3Cr4+ → 2Cr3+ + Cr6+ in association with the 6s-p hybridization on the Pb2+ is responsible for the insulating ground state of PbCrO3 at ambient pressure and the charge disproportionation phase is suppressed under pressure to give rise to a metallic phase at high pressure. The model is well supported by density function theory plus the correlation energy U (DFT+U) calculations. Fil: Cheng, Jinguang. University Of Texas At Austin; Estados Unidos. Chinese Academy Of Sciences; República de China. University of Tokyo. Institute for Solid State Physics; Japón Fil: Kweon, K. E.. University Of Texas At Austin; Estados Unidos Fil: Larregola, Sebastian Alberto. University Of Texas At Austin; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis. Instituto de Investigaciones en Tecnología Química; Argentina Fil: Ding, Yang. Argonne National Laboratory; Estados Unidos Fil: Shirako, Y.. University Of Texas At Austin; Estados Unidos Fil: Marshall, L. G.. University Of Texas At Austin; Estados Unidos. Northeastern University; Estados Unidos Fil: Li, Z. Y. . University Of Texas At Austin; Estados Unidos Fil: Li, X.. University Of Texas At Austin; Estados Unidos Fil: Dos Santos, António M.. Oak Ridge National Laboratory. Quantum Condensed Matter Division; Estados Unidos Fil: Suchomel, M. R.. Argonne National Laboratory; Estados Unidos Fil: Matsubayashi, K.. University of Tokyo. Institute for Solid State Physics; Japón Fil: Uwatoko, Y.. University of Tokyo. Institute for Solid State Physics; Japón Fil: Hwang, G. S.. University Of Texas At Austin; Estados Unidos Fil: Goodenough, John B.. University Of Texas At Austin; Estados Unidos Fil: Zhou, J. S.. University Of Texas At Austin; Estados Unidos

Using microbeam hard X-ray photoelectron spectroscopy, we clarified the valence-band electronic structures and chemical states of platinum-group metal (Ru, Ir, and Pt) pernitrides, which have been synthesized in supercritical nitrogen fluid under extremely high pressures and temperatures. Their nitrogen contents relative to the platinum-group metal are estimated to be 2 from the photoemission intensity, which is consistent with the studies reported to date. The observed valence-band structures agree quite well with theoretically predicted structures for the pyrite-type PtN2, arsenopyrite-type IrN2, and marcasite-type RuN2. The origin of their extremely large bulk moduli is discussed based on the current results of the valence-band structures and core-level chemical shifts.

Thermal effect on the orthorhombic crystal structure (Cmcm) of the correlated 4d post-perovskite CaRhO3 was investigated by an X-ray powder diffraction method between 60 K and 300 K. Anisotropic thermal evolution of the structure was observed over the temperature range, and in addition, an anomalous change of the lattice parameters was detected at the antiferromagnetic transition temperature of 90 K, indicating possible correlations between the lattice and the magnetic order.

The first Ruddlesden-Popper type layered cobalt oxyfluoride, Sr(2)CoO(3)F, has been synthesized under a pressure of 6 GPa at 1700 °C and shown to adopt a K(2)NiF(4)-type structure with distorted square pyramidal coordination around Co and with O/F disorder at the apical sites.

The polycrystalline MO2's (HP-PdF2-type MO2, M = Rh, Os, Pt) with high-pressure PdF2 compounds were successfully synthesized under high-pressure conditions for the first time, to the best of our knowledge. The crystal structures and electromagnetic properties were studied. Previously unreported electronic properties of the polycrystalline HP-PdF2-type RuO2 and IrO2 were also studied. The refined structures clearly indicated that all compounds crystallized into the HP-PdF2-type structure, M(4+)O(2-)2, rather than the pyrite-type structure, M(n+)(O2)(n-) (n4). The MO2 compounds (M = Ru, Rh, Os, Ir) exhibited metallic conduction, while PtO2 was highly insulating, probably because of the fully occupied t2g band. Neither superconductivity nor a magnetic transition was detected down to a temperature of 2 K, unlike the case of 3d transition metal chalcogenide pyrites.

Ferroelectric A-site-ordered double perovskite CaMnTi2O6 is prepared from equimolar mixtures of MnTiO3 and CaTiO3 in Au (for single crystals) and Pt capsules (for polycrystalline material) under high-pressure (TRY cubic multianvil press, 1200-1700 °C, 7 GPa, 0.5 h) followed by annealing (N2 atmosphere, 500 °C, 6 h).

BaIrO3 adopts the 9R polytype structure if it is synthesized at ambient pressure. High-pressure and high-temperature treatments up to 10 GPa have led to other 5H and 6H polytype phases, which are quenchable to the ambient condition. However, the single-phase 3C perovskite, the end member of polytypes, has not been obtained so far. Here we report the high-pressure synthesis of BaIrO3 perovskite under 25 GPa and 1150 degrees C. Rietveld refinement on the powder x-ray diffraction pattern revealed that this new compound crystallizes in a tetragonal I4/mcm structure rather than the expected cubic Pm-3m structure. The new perovskite is a Pauli paramagnetic metal with a Fermi liquid ground state, i.e., rho proportional to T-2 below 6 K. The availability of BaIrO3 perovskite also allows completion of the structure-physical property evolution in the AIrO(3) perovskites (A = Ca, Sr, Ba). The Fermi energy located in bands originated from Ir: 5d and O: 2p electrons are found to be very sensitive to the change of crystal structure.

In continuation of the series of perovskite oxides that includes 3d(4) cubic BaFeO3 and 4d(4) cubic BaRuO3, 5d(4) cubic BaOsO3 was synthesized by a solid-state reaction at a pressure of 17 GPa, and its crystal structure was investigated by synchrotron powder X-ray diffraction measurements. In addition, its magnetic susceptibility, electrical resistivity, and specific heat were measured over temperatures ranging from 2 to 400 K. The results establish a series of d(4) cubic perovskite oxides, which can help in the mapping of the itinerant ferromagnetism that is free from any complication from local lattice distortions for transitions from the 3d orbital to the 5d orbital. Such a perovskite series has never been synthesized at any d configuration to date. Although cubic BaOsO3 did not exhibit long-range ferromagnetic order unlike cubic BaFeO3 and BaRuO3, enhanced feature of paramagnetism was detected with weak temperature dependence. Orthorhombic CaOsO3 and SrOsO3 show similar magnetic behaviors. CaOsO3 is not as conducting as SrOsO3 and BaOsO3, presumably due to impact of tilting of octahedra on the width of the t2g band. These results elucidate the evolution of the magnetism of perovskite oxides not only in the 5d system but also in group 8 of the periodic table.

High-pressure stability, ambient metastability, and high-pressure crystal chemistry of chemical bonds of marcasite-type RhN2 have been investigated using a laser-heated diamond-anvil cell up to a pressure of 70.6 GPa. High-pressure in-situ X-ray diffraction and Raman scattering measurements revealed that the marcasite-type RhN2 structure is stable up to 70.6 GPa and exhibited an order of axial compressibility of βc > βb > βa. This indicates that single bonded nitrogen dimer (N-N) plays an important role in the incompressibility of a- and b-axes than in that of the c-axis and stabilizes the marcasite-type structure at high-pressure. Field emission scanning electron microscopic analysis in combination with the energy dispersive X-ray spectroscopic measurements and the result of our previous study indicates that the marcasite-type RhN2 can be quenched to ambient pressure when the grain size is less than 100 nm. Our study together with other previous studies indicates that the ambient metastability of 4d plat...

Correction for ‘New layered cobalt oxyfluoride, Sr2CoO3F’ by Yoshihiro Tsujimoto et al., Chem. Commun., 2011, 47, 3263–3265.

We investigated the doping effects of magnetic and nonmagnetic impurities in single-crystalline $p$-type Ba${}_{0.5}$K${}_{0.5}$Fe${}_{2\ensuremath{-}2x}{M}_{2x}$As${}_{2}$ ($M$ = Mn, Ru, Co, Ni, Cu, and Zn) superconductors. The superconductivity is maintained robustly with the impurity Ru, and weakly with the impurities Mn, Co, Ni, Cu, and Zn. However, the present ${T}_{c}$ suppression rate of both magnetic and nonmagnetic impurities remains much lower than what was expected for the s${}_{\ifmmode\pm\else\textpm\fi{}}$-wave model. The temperature dependence of resistivity data shows an obvious low-$T$ upturn for the crystals doped with high levels of impurity, which is due to the occurrence of localization. Thus, the relatively weak ${T}_{c}$ suppression effect from Mn, Co, Ni, Cu, and Zn is considered to be a result of localization rather than the pair-breaking effect in the ${s}_{\ifmmode\pm\else\textpm\fi{}}$-wave model.

The postspinel mineral MgAl(2)O(4) exists only under the severe pressure conditions in the subducted oceanic lithosphere in the Earth's deep interior. Here we report that its analogous oxide CdRh(2)O(4) exhibits a structural transition to a quenchable postspinel phase under a high pressure of 6 GPa at 1400 °C, which is within the general pressure range of a conventional single-stage multianvil system. In addition, the complex magnetic contributions to the lattice and metal nonstoichiometry that often complicate investigations of other analogues of MgAl(2)O(4) are absent in CdRh(2)O(4). X-ray crystallography revealed that this postspinel phase has an orthorhombic CaFe(2)O(4) structure, thus making it a practical analogue for investigations into the geophysical role of postspinel MgAl(2)O(4). Replacement of Mg(2+) with Cd(2+) appears to be effective in lowering the pressure required for transition, as was suggested for CdGeO(3). In addition, Rh(3+) could also contribute to this reduction, as many analogous Rh oxides of aluminous and silicic minerals have been quenched from lower-pressure conditions.

High-pressure structural phase transitions in NaNiF(3) and NaCoF(3) were investigated by conducting in situ synchrotron powder X-ray diffraction experiments using a diamond anvil cell. The perovskite phases (GdFeO(3) type) started to transform into postperovskite phases (CaIrO(3) type) at about 11-14 GPa, even at room temperature. The transition pressure is much lower than those of oxide perovskites. The anisotropic compression behavior led to heavily tilted octahedra that triggered the transition. Unlike oxide postperovskites, fluoropostperovskites remained after decompression to 1 atm. The postperovskite phase in NaCoF(3) broke down into a mixture of unknown phases after laser heating above 26 GPa, and the phases changed into amorphous ones when the pressure was released. High-pressure and high-temperature experiments using a multianvil apparatus were also conducted to elucidate the phase relations in NaCoF(3). Elemental analysis of the recovered amorphous samples indicated that the NaCoF(3) postperovskite disproportionated into two phases. This kind of disproportionation was not evident in NaNiF(3) even after laser heating at 54 GPa. In contrast to the single postpostperovskite phase reported in NaMgF(3), such a postpostperovskite phase was not found in the present compounds.

The title compound, the first Ruddlesden—Popper type layered cobalt oxyfluoride, is synthesized by high-temperature/high-pressure reaction of a stoichiometric mixture of SrO2, Co, and SrF2 (Pt capsule, 6 GPa, 1700 °C, 1.5 h).

A quasi-one-dimensional magnetism was discovered in the post-perovskite CaRuO${}_{3}$ (Ru${}^{4+}$: $4{d}^{4}$, Cmcm), which is isocompositional with the perovskite CaRuO${}_{3}$ (Pbnm). An antiferromagnetic (AFM) spin-chain function with \ensuremath{-}$J$/${k}_{\mathrm{B}}$ $=$ 350 K reproduces the experimental curve of the magnetic susceptibility vs temperature well, suggesting long-range AFM correlations. The anisotropic magnetism is probably owed to the ${d}_{\mathit{yz}}$-$2{p}_{\mathrm{\ensuremath{\pi}}}$-${d}_{\mathit{zx}}$ and ${d}_{\mathit{zx}}$-$2{p}_{\mathrm{\ensuremath{\pi}}}$-${d}_{\mathit{yz}}$ superexchange bonds along the $a$ axis. The Sommerfeld coefficient of the specific heat is fairly small, 0.16(2) mJ mol${}^{\ensuremath{-}1}$ ${\mathrm{K}}^{\ensuremath{-}2}$, indicating that the magnetism reflects the localized nature of the 4$d$ electrons. This is an observation of an integer ($S$ $=$ 1) spin-chain AFM in the 4$d$ electron system.

A high-quality polycrystalline sample of the correlated 4d post-perovskite CaRhO(3) (Rh(4+): 4d(5), S(el) = 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 approximately 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.

Ferroelectricity, piezoelectricity, pyroelectricity, and second-order nonlinear optical behavior are technologically important. Because these properties are attributable to the noncentrosymmetric (NCS) structure[1], the search for materials exhibiting such characteristics must begin with a search of NCS materials. Among them, LiNbO3-type (LN-type) compounds with a chemical formula of ABX3 exhibit NSC structures with hexagonal polar space group R3c whose BX6 octahedra three-dimensionally share their corners the same as perovskite-type compounds[2]. In LN-type compounds, the A cation - B cation repulsion directs the spontaneous polarization along c-axis(Fig. 1). Therefore, we might find attractive functional properties by the selection of constituent ions based on their having a naturally occurring polar LN-type structure attributable to the cation-cation repulsion. With the ideas mentioned above, we have investigated the high-pressure synthesis and characterization of novel LN-type oxides such as ZnSnO3, PbNiO3, CdPbO3 as well as known MnMO3 (M = Ti, Sn). Recently, we have successfully synthesized a polar LN-type titanate ZnTiO3 (LN-ZTO) under high pressure and high temperature [3]. The first principles calculation indicates that LN-ZTO is a meta-stable 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 reveals that LN-ZTO exhibits greater intra-distortion of the TiO6 in LN-ZTO than that of the SnO6 in LN-type ZnSnO3 (LN-ZSO). The estimated spontaneous polarization are greater than those of LN-ZSO, which is attributed to the great displacement of Ti along c-axis and the greater Born effective charge of Ti (+6.1) than that of Sn (+4.1). Furthermore, the spontaneous polarization of LN-ZTO is greater than that of LiNbO3, indicating that LN-ZTO, like LiNbO3, is a candidate ferroelectric material with high performance. The second harmonic generation (SHG) response of LN-ZTO is 24 times greater than that of LN-ZSO. The findings indicate that the intra-octahedral distortion, spontaneous polarization, and SHG response are caused by the stabilization of the polar LN-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+. We also discuss the relationship between the intra-distortion of BO6 and polarity in several LN-type oxides.

High-pressure phase transitions in CaRhO3 were examined using a multianvil apparatus up to 27 GPa and 1930 oC. CaRhO3 perovskite transforms to post-perovskite via a monoclinic intermediate phase with increasing pressure. Volume changes for the transitions of perovskite – intermediate phase and of intermediate phase – post-perovskite are -1.1 and -0.7 %, respectively. CaRhO3 post-perovskite is the fourth quenchable post-perovskite oxide found so far. By high-temperature calorimetric experiments, enthalpy of the perovskite – post-perovskite transition in CaRuO3 was measured as 15.2±3.3 kJ/mol. Combining the datum with those of CaIrO3, it is shown that CaIrO3 perovskite is energetically less stable than CaRuO3 perovskite. This is consistent with the fact that orthorhombic distortion of CaIrO3 perovskite is larger than CaRuO3, as indicated with the tilt-angle of octahedral framework of perovskite structure. The transition pressure from perovskite to post-perovskite in CaBO3 (B = Ru, Rh, Ir) increases almost linearly with decreasing the tilt-angle, suggesting that the perovskite – post-perovskite transition may result from instability of the perovskite structure with pressure.

CaRuO3 post-perovskite which has quasi-two-dimensional lattice shows one dimensional antiferromagnetism such as Bonner-Fisher type above 400 K. The Neel temperature, TN, is around 270 K.