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High-pressure RMn3O6 manganites (belonging to a family of A-site columnar-ordered quadruple perovskites A2A′A″B4O12, where A′ is a site with a square-planar coordination and A″ is a site with a tetrahedral coordination) are prone to cation non-stoichiometry: they are rare-earth-deficient, R1−xMn3+xO6, for R = Ho, Y, Er, and Tm and manganese-deficient, R1+xMn3−xO6, for R = Gd. Here we investigated their crystal structures using single-crystal X-ray diffraction and synchrotron X-ray powder diffraction at room temperature. We found that the rare-earth deficiency is formed by doping of Mn2+ into the A site: [Er3+1.78Mn2+0.22]A[Mn3+]A′[Mn2+]A′′[Mn3+2]B1[Mn3.61+2]B2O12. The manganese deficiency is realized through doping of a small amount of Gd3+ into the A″ site: [Gd3+2]A[Mn3+]A′[Mn2+0.87Gd3+0.13]A′′[Mn3+2]B1[Mn3.44+2]B2O12. They all crystallize in space group Pmmn with layered charge ordering at the B sites. They are structurally related to CaFeTi2O6. Cation non-stoichiometry is supported by variations of the oxidation states of manganese at one of the B sites.

A new polymorph of the triple perovskite Ba3CuOs2O9, which usually exists in the orthorhombic phase, was synthesized under high-pressure and high-temperature conditions at 6 GPa and 1100 °C. Under the synthetic condition, Ba3CuOs2O9 crystallizes into a hexagonal structure (P63/mmc) with a = 5.75178(1) A and c = 14.1832(1) A, and undergoes a 1.36% increment in density, compared to that of the orthorhombic phase. Although Ba3CuOs2O9 maintains its 6 H perovskite-type structure, the distribution of Cu and Os atoms are dramatically altered; (Cu)4a(Os,Os)8f transits to (Os)2a(Cu,Os)4f ordering over the corner- and face-sharing sites, respectively. The hexagonal Ba3CuOs2O9 exhibits a ferrimagnetic transition at 290 K, which is in stark contrast to the antiferromagnetic transition at 47 K exhibited by the orthorhombic Ba3CuOs2O9. The enhanced transition temperature is most likely due to the strongly antiferromagnetic Os5+–O–Os5+ bonds and the moderately antiferromagnetic Os5+–O–Cu2+ bonds, the angles of which are both approximately 180°. The 290 K ferrimagnetic transition temperature is the highest reported for triple-perovskite osmium oxides. Besides, the coercive field is greater than 70 kOe at 5 K, which is remarkable among the coercive fields of magnetic oxides.

The structure of a polycrystalline sample of SrOsO 3 has been investigated using powder neutron diffraction from 5 to 300 K, and powder synchrotron X-ray diffraction from 80 to 870 K. At low temperatures SrOsO 3 is orthorhombic in Pbnm and heating results in a sequence of phase transition transitions Pbnm → Imma → I 4 / mcm → Pm 3 m . This behavior is compared to that of other Sr containing perovskites. Comparison of the transition temperatures in Sr B O 3 perovskites shows that the tolerance factor alone does not determine the temperature at which the cubic phase is stabilized but rather the electronic configuration of the B-site cation appears to be significant.

High-pressure crystal growth and synthesis of selected solid-state osmium oxides, many of which are perovskite-related types, are briefly reviewed, and their magnetic and electrical properties are introduced. Crystals of the osmium oxides, including NaOsO 3 , LiOsO 3 , and Na 2 OsO 4 , were successfully grown under high-pressure and high-temperature conditions at 6 GPa in the presence of an appropriate amount of flux in a belt-type apparatus. The unexpected discovery of a magnetic metal–insulator transition in NaOsO 3 , a ferroelectric-like transition in LiOsO 3 , and high-temperature ferrimagnetism driven by a local structural distortion in Ca 2 FeOsO 6 may represent unique features of the osmium oxides. The high-pressure and high-temperature synthesis and crystal growth has played a central role in the development of solid-state osmium oxides and the elucidation of their magnetic and electronic properties toward possible use in multifunctional devices.

BaPr2ZnO5, BaSm2ZnO5, and BaEu2ZnO5 – a series of 4f magnetic insulators comprising the Shastry-Sutherland lattice – were synthesized via a solid-state reaction under high-pressure and high-temperature conditions. The magnetic behaviors are well characterized by the localized 4f electrons of each Ln3+ (= Pr, Sm, Eu) under the influence of the crystal-electric field of the surrounding ions. The magnetic susceptibility and heat capacity measurements of BaPr2ZnO5 (Pr3+; 4f2 3H4) indicate the splitting of the ground state J-multiplet due to the crystal-electric field. BaSm2ZnO5 (Sm3+; 4f5 6H5/2) is a strong Van Vleck paramagnet, while BaEu2ZnO5 is non-magnetic due to the 7F0 ground state (Eu3+; 4f6 7F0). The series of new oxides enriches a group of the Shastry-Sutherland lattice materials and helps to develop a range of two-dimensional quantum materials.

A new compositional double perovskite oxide Ba{sub 2}CuOsO{sub 6} was synthesized under high-pressure (6 GPa) and high-temperature (1500 °C) conditions. The polycrystalline Ba{sub 2}CuOsO{sub 6} was characterized by synchrotron X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility, isothermal magnetization, and specific heat measurements. The oxide crystallizes in a double-perovskite structure with an I4/m space group, in which Os(VI) and Cu(II) are ordered in the perovskite B-site. Ba{sub 2}CuOsO{sub 6} is electrically insulating with an activation energy of 0.813(2) eV and shows antiferromagnetic-like characteristics at temperatures of ∼55 K and ∼70 K. The results of the first-principle calculation suggested that the spin–orbit interaction of Os(VI) plays a substantial role in the insulating state. The Jahn–Teller distortion of CuO{sub 6} octahedra influences the magnetic characteristics with regard to possible two-dimensional magnetic correlations. - Graphical abstract: A new compositional double perovskite oxide Ba{sub 2}CuOsO{sub 6} synthesized by a high-pressure (6 GPa) and high-temperature (1500 °C) method. - Highlights: • A new compositional double perovskite oxide Ba{sub 2}CuOsO{sub 6} was synthesized. • Ba{sub 2}CuOsO{sub 6} is electrically insulating and antiferromagnetic below ∼70 K. • The Jahn–Teller distortion of CuO{sub 6} has relevance to possible magnetic anisotropy.

The effects of substituting Co on the spin-chain compound Sr3Co2O6 with Zn were investigated by synchrotron X-ray diffraction, magnetic susceptibility, isothermal magnetization, and specific heat measurements. To the best of our knowledge, this is the first report to describe the successful substitution of Co in Sr3Co2O6 with Zn. The substitution was carried out by a method involving high pressures and temperatures to obtain Sr3CoZnO6, which crystalized into a K4CdCl6-derived rhombohedral structure with a space group of R-3c, similar to the host compound. With the Zn substitution, the Ising-type magnetic anisotropy of the host compound remarkably reduced; the newly formed Sr3CoZnO6 became magnetically isotropic with Heisenberg-type characteristics. This could probably be ascribed to the establishment of a different interaction pathway, –Co4+(S=1/2)–O–Zn2+(S=0)–O–Co4+(S=1/2)–. Details of the magnetic properties of Zn substituted Sr3Co2O6 were reported.

Single crystals of the osmium-containing compound Ca3OsO6 have been successfully grown under high-pressure conditions, for the first time. The crystal structure of Ca3OsO6 were characterized as an ordered double-perovskite structure of space group P2(1)/n with the Ca and Os atoms being fully ordered at the perovskite B-site. The electromagnetic analysis shows that the crystal exhibits a semiconductor-like behavior below 300 K and undergoes an antiferromagnetic transition at 50 K. (C) 2013 Elsevier Inc. All rights reserved.

The superconducting and lattice properties of {delta}-MoC{sub 0.681} were studied by electromagnetic measurements, synchrotron X-ray diffraction, neutron diffraction, and electron diffraction. The superconducting properties (T{sub c}=12 K) of {delta}-MoC{sub 0.681} were well characterized by a weak coupling model. The carbon vacancies present in the host cubic structure were found to be robust, although the material was synthesized from stoichiometric carbon and Mo powder under a high-pressure of 6 GPa. A thermodynamically-stable structure with ordered vacancies did not account for the robust features of {delta}-MoC{sub 0.681} since the vacancies are unlikely to be ordered in long range in the host structure. A model based on inherent phonon instability theoretically predicted for a stoichiometric MoC phase might be responsible for the robust features of {delta}-MoC{sub 0.681}. - Graphical Abstract: The cubic molybdenum carbide shows an excellent superconductivity with robust carbon vacancies. Inherent phonon instability theoretically predicted for a stoichiometric MoC phase might be responsible for the vacancies rather than a thermodynamically-stable structure with vacancies ordering. Highlights: Black-Right-Pointing-Pointer The 12 K superconductivity is well characterized by a weakly coupling model. Black-Right-Pointing-Pointer Carbon vacancies are robust and disordered in the cubic host structure. Black-Right-Pointing-Pointer Inherent phonon instability might be responsible for the robust carbonmore » vacancies in {delta}-MoC{sub 0.681}.« less

Na2OsO4 crystals were grown by a NaCl flux method under high pressure. It crystallizes in the Ca2IrO4-type structure without having additional elements or metal vacancies, which are usually accommodated. It appears that Na2OsO4 is a metal-stoichiometric Ca2IrO4-type compound never been synthesized to date. Na2OsO4 has the octahedral environment of Os6+O6 so that the electronic configuration is 5d2, suggesting the magnetic S=1 ground state. However, magnetization, electrical resistivity, and specific heat measurements indicated that the non-magnetic S=0 state is much likely for Na2OsO4 than the S=1 state. Band structure calculations and the structure analysis found that the disagreement is probably due to the statically uniaxial compression of the OsO6 octahedra, resulting in splitting of the t 2 g band.

The cross-linked chain cobalt oxychloride Ba{sub 5}Co{sub 5}ClO{sub 13} is reported. Single crystals were obtained by a flux method with BaCl{sub 2}. A hexagonal unit cell (P6{sub 3}/mmc, a=5.6980(8) {angstrom} and c=24.469(5) {angstrom}) was found. The +3 and +4 valence cobalt ions were formally distributed into octahedral and tetrahedral sites coordinated by oxide ions. The compound was electrically insulating with a gap of 0.25 eV along the chain. Antiferromagnetism was found, with substantial ferromagnetic character, suggesting that the magnetic ground state is complex. Copyright 2001 Academic Press.

The iron oxycarbonate Sr 4 Fe 2 O 6 CO 3 is reported. The crystal structure and magnetic order were determined by magnetic susceptibility, powder neutron diffraction, and neutron scattering studies. The structure is tetragonal between 10 and 400 K ( I 4/mmm, a =3.88907(4) A and c =27.9818(4) A at 295 K), and is related to a 4:3 type Ruddlesden–Popper phase with CO 3 plaques in place of the middle layer of transition metal octahedra. The three-dimensional magnetic ordering transition temperature is 361 K. The magnetic order is antiferromagnetic within the FeO 2 /SrO/SrO/FeO 2 blocks and ferromagnetic between blocks.

TB–LMTO–ASA band structure calculations within the local spin density approximation have been performed to explain the magnetic and transport properties of BaCoO3. The calculations predict a magnetic and metallic ground state as energetically favored. BaCoO3 shows no long-range magnetic ordering, however, and only poor conductivity. The magnetic energy is low and the compound shows glassy susceptibility behavior at low temperatures. From the band structure we find Mott–Hubbard localization to be unlikely, and instead propose Anderson localization as a possible origin of the observed behavior. Calculations on slightly distorted structures exclude the possibility of a Peierls distortion.

The hexagonal perovskite solid solution Ba 1− x Sr x CoO 3 (0≤ x ≤0.5) was synthesized by treatment of cubic perovskite precursors at 500°C in high-pressure oxygen. The structure consists of parallel chains of face-sharing CoO 6 octahedra and alkaline-earth ion separators. All materials were found to be semiconducting. Seebeck coefficient measurements indicate that transport is by both electrons and holes. The slopes of the magnetic susceptibility vs temperature data suggest that Co is in the low-spin S =1/2 electronic configuration. The positive Curie–Weiss Θ w 's indicate a predominantly ferromagnetic spin interaction, and a complex magnetic state is seen at low temperature in the temperature- and field-dependent magnetic data.

New layered Co oxides of nominal formula Sr 2 ( Ln 0.8 Ca 0.2 ) Co 2 O 6 ( Ln =Sm, Eu, Gd, Tb, Dy, Ho, and Y) are reported. Single-phase polycrystalline samples were obtained at compositions Sr 2 Y 1− x Ca x Co 2.5+ 2 O 6− δ (0.2≤ x ≤0.5; 0≤ δ ≤0.24), Sr 2 Y 1− x Ca x Co 3.4+ 2 O 6+ δ ′ (0.2≤ x ≤0.5; 0.62≤ δ ′≤0.79), and Sr 2 Dy 0.8 Ca 0.2 Co 2 O 6.09 . Powder X-ray and neutron diffraction, thermogravimetric analysis, magnetic susceptibility, and ac resistivity measurements were used to characterize the samples. The tetragonal unit cell for Sr 2 Y 0.8 Ca 0.2 Co 2 O 6.00 ( I 4/ mmm ; a =3.82765(6) A, and c =19.5795(3) A) is comparable to that of the double layer superconducting copper oxide La 2− x Sr x CaCu 2 O 6 . A long-range antiferromagnetic (AF) ordered state below about 300 K is found for Sr 2 Y 1− x Ca x Co 2.5+ 2 O 6− δ , and a magnetically glassy state below about 40 K for the oxidized AF phases. All materials are electrically insulating.