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A new hexagonal perovskite-type oxide Ba8Ta4Ru8/3Co2/3O24 was synthesized by the solid-state method at 1573 K and characterized by electron diffraction (ED), time-of-flight (TOF) neutron powder diffraction, and magnetic susceptibility. Structure parameters of Ba8Ta4Ru8/3Co2/3O24 were refined by the Rietveld method from the TOF neutron powder diffraction data on the basis of space group P63/mcm and lattice parameters a=10.0075(1) Å and c=18.9248(2) Å as obtained from the ED data (Z=3). The crystal structure of Ba8Ta4Ru8/3Co2/3O24 consists of 8-layered (cchc)2 close-packed stacking of BaO3 layers along the c-axis. Corner-shared octahedra are filled by Ta only and face-shared octahedra are statistically occupied by Ru, Co, and vacancies. Similar compounds Ba8Ta4Ru8/3M2/3O24 with M=Ni and Zn were also prepared. Magnetic susceptibility measurements showed no magnetic ordering down to 5 K. [Copyright &y& Elsevier]

Properties of Sr2Cu(PO4)2 and Ba2Cu(PO4)2 having [Cu(PO4)2]∞ linear chains in their structures with Cu–O–P–O–Cu linkages were studied by magnetic susceptibility (T=2–400 K, H=100 Oe) and specific heat measurements (T=0.45–21 K). Magnetic susceptibility versus temperature curves, χ(T), showed broad maxima at TM=92 K for Sr2Cu(PO4)2 and TM=82 K for Ba2Cu(PO4)2 characteristic of quasi-one-dimensional systems. The χ(T) data were excellently fitted by the spin susceptibility curve for the uniform S=1/2 chain (plus temperature-independent and Curie–Weiss terms) with g=2.153(4) and J/kB=143.6(2) K for Sr2Cu(PO4)2 and g=2.073(4) and J/kB=132.16(9) K for Ba2Cu(PO4)2 (Hamiltonian H=JΣSiSi+1). The similar J/kB values were obtained from the specific heat data. No anomaly was observed on the specific heat from 0.45 to 21 K for both compounds indicating that the temperatures of long-range magnetic ordering, TN, were below 0.45 K. Sr2Cu(PO4)2 and Ba2Cu(PO4)2 are an excellent physical realization of the S=1/2 linear chain Heisenberg antiferromagnet with kBTN/J<0.34% together with Sr2CuO3 (kBTN/J&ap;0.25%) and γ-LiV2O5 (kBTN/J<0.16%). Sr2Cu(PO4)2 and Ba2Cu(PO4)2 were stable in air up to 1280 and 1150 K, respectively. [Copyright &y& Elsevier]

Ca 9.5–1.5 x Bi x Cd(VO 4 ) 7 (0 ≤ x ≤ 1) solid solutions with the whitlockite-type structure (SG R 3 c ) were synthesized by a standard solid-state method in air. Structures of Ca 9.5–1.5 x Bi x Cd(VO 4 ) 7 ( x = 0.167, 0.5, 0.833) were refined by the Rietveld method from synchrotron powder X-ray diffraction data. Nonlinear optical properties of the whitlockite-type compounds can be designed and increased by an order of magnitude through appropriate isovalent and aliovalent substitutions for Ca 2+ cations. Dielectric and temperature second harmonic generation investigations revealed the presence of a reversible ferroelectric phase transition in the range from 1331 K to 1055 K. The phase transition temperature monotonically decreases while nonlinear optical activity of Ca 9.5–1.5 x Bi x Cd(VO 4 ) 7 strongly increases with increasing Bi 3+ content. [ABSTRACT FROM AUTHOR]

Highlights: [•] The detailed P–T phase diagram of BiMnO3 was established. [•] We found three monoclinic modifications of BiMnO3 at pressure and temperature. [•] A suppression of monoclinic C2/c phase have been observed under pressure. [•] We found a new orthorhombic Imma phase of BiMnO3 at P >20GPa. [Copyright &y& Elsevier]

Abstract: A new inverse spinel ScMn2O4 has been synthesized and characterized by measurements of structural and physical properties. The crystal structure of ScMn2O4, similar with the spinel Mn3O4, is made up of Mn2+ located at tetrahedral site and Mn3+/Sc3+ ions randomly located at the octahedral site. Experimental results of magnetic susceptibility and heat capacity demonstrate that ScMn2O4 undergoes a ferrimagnetic phase transition at the temperature of about 58K. Extensive analyses on the data obtained from structural refinement, electronic structural calculation and EELS spectra measurement suggests that substitution of Sc for Mn in MnO6 octahedron could greatly suppress Jahn–Teller distortions in comparison with what observed in Mn3O4. [Copyright &y& Elsevier]

Abstract: 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 5d 2, 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 band. [Copyright &y& Elsevier]

Abstract: Submillimeter and millimeter wave ESR measurements of spin gap systems SrCu2(PO4)2 and PbCu2(PO4)2, which have four kinds of dimers, have been performed to investigate the magnetic properties of spin gap systems using the pulsed magnetic field up to 35T. The observed ESR spectra of powder sample SrCu2(PO4)2 show sharp and single peak in the temperature range from 4.2 to 80K. The anisotropy of the g-values turned out to be very small compared to the usual anisotropic powder spectra of copper compounds. The dynamical properties will be discussed from the temperature dependence measurements. [Copyright &y& Elsevier]

Abstract: Oxygen vacant superconductors LaFeAsO1− δ were synthesized under a high-pressure condition. A bell-shaped feature in Tc vs. δ was observed for LaFeAsO1− δ as well as TbFeAsO1− δ . The optimized Tc was achieved at δ of 0.15, being comparable with that for TbFeAsO1− δ . The relatively wide δ window of LaFeAsO1− δ may merit scientific and technical studies of high-Tc superconductivity. [ABSTRACT FROM AUTHOR]