Solid State Phenomena Vol. 170

Abstract: The Co2Sm2W3O14 compound crystallizes in the orthorhombic system, and melts congruently at 1443 K. The magnetic measurements showed that Co2Sm2W3O14 is a paramagnet in the temperature range 4.2-225 K showing both the residual magnetic interactions since the paramagnetic Curie-Weiss temperature   0 and the uncompensated temperature independent contributions of magnetic susceptibility since 0  0. The Brillouin fit of the Landé factor revealed an increase of the orbital contribution to the total magnetic moment of the compound what seems to be responsible for its hard and spontaneous magnetization at low temperatures.

Abstract: Electrical resistivity dips in the temperature range 269-287 K and n-type conductivity below 415 K for solid solutions of MoO3 in SbVO5 with general formula SbxVyMozOt are observed. The electrical resistivity anomalies are interpreted as due to conduction of small-polarons, generated here as electrons together with distortions of their associated defective oxygen lattice and/or alternatively based on the crossover of electronic or polaronic states.

Abstract: A high spin (HS) – low spin (LS) transition has been discovered in the Co[Cr0.5Ga1.5]S4 spinel, where the Co ions occupy tetrahedral sites and the Cr and Ga ions octahedral ones. The latter are diluted by the non-magnetic Ga-ions. Application of magnetic fields revealed ferrimagnetic order with a Curie temperature TC = 126 K, a strong suppression of the magnetic susceptibility () and a slight shift of TC to lower temperatures. A cusp at 15.6 K on the ac (T) curve suggests a spin frustration of the re-entrant type. Characteristic for the HS-LS transition is an inflection point at 150 K on the 1/(T) curve, a lack of the Curie-Weiss region above TC and a small value of the magnetization, 4.76 emu/g at 4.4 K and at a magnetic field of 57.5 kOe.

Abstract: The atomic site distribution of the complex σ-phase structure (P42/mnm) has been studied using density functional theory (within the EMTO and WIEN2k codes) applying the cluster expansion method in a mean field approximation at finite temperatures. We found that at low temperatures Fe atoms predominantly occupy the icosahedrally coordinated (A,D) sites, Cr atoms prefer the (B,E) sites with the high coordination numbers, while the C site remains mixed. However, at higher temperature close to 1000 K all occupations become more and more mixed and reproduce well the available experimental data.

Abstract: New pseudo-hollandite chromium tellurides, ACr5Te8 (A = K, Cs and Rb), have been synthesized. KCr5Te8 is isostructural (type-A; space group C2/m) to ACr5S8, while RbCr5Te8 and CsCr5Te8 crystallize in a different structure (type-B; space group C2/m). All compounds show ferromagnetic transition, in contrast to antiferromagnetic transition in pseudo-hollandite chromium sulfides and selenides. The ferromagnetism of ACr5Te8 would be related to long Cr-Cr distances, band structure or itinerancy.

Abstract: Electronic structure of solar-energy related crystals of CuInS2 and CuAlS2 has been characterized using thermoreflectance (TR) measurement in the energy range between 1.25 and 6 eV. The TR measurements were carried out at room (~300 K, RT) and low (~30 K, LT) temperatures. A lot of interband transition features including band-edge excitons and higher-lying interband transitions were simultaneously detected in the low-temperature TR spectra of CuInS2 and CuAlS2. The energies of band-edge excitonic transitions at LT (RT) were analysed and determined to be =1.545 (1.535) and =1.554 eV (1.545 eV) for CuInS2, and =3.514 (3.486), =3.549 (3.522), and =3.666 eV (3.64 eV) for CuAlS2, respectively. The band-edge transitions of the and excitons are originated from the sulfur pp transitions in CuInS2 and CuAlS2 separated by crystal-field splitting. Several high-lying interband transitions were detected in the TR spectra of CuInS2 and CuAlS2 at LT and RT. Transition origins for the high-lying interband transitions are evaluated. The dependence of electronic band structure in between the CuInS2 and CuAlS2 is analysed and discussed.

Abstract: We succeeded in synthesizing single crystals of a novel nickel sulfate Ni2-δSO5 by a hydrothermal method. A single-crystal X-ray diffraction revealed a tetragonal structure with lattice constants, a = 5.184 Å and c = 12.91 Å. In this structure, one-dimensional chains composed of face-shared NiO6 octahedra elongate along the a axis and the b axis alternately, constructing a ‘log-cabin’ type framework where neighbor chains lying orthogonally to each other are connected by SO4 tetrahedra. A detailed refinement of the structure suggested that the site occupancy of Ni is only 63%, corresponding to δ ≈ 2/3. Furthermore, X-ray oscillation photographs exhibit diffuse-scattering patterns probably arising from a short-range order of the Ni defects. Magnetic susceptibility revealed an antiferromagnetic transition accompanied by a weak ferromagnetism at 17 K.

Abstract: We have discovered a novel compound Na0.12CrO2Ge0.18Ox•yH2O using a hydrothermal method. Its powder X-ray diffraction reveals a monoclinic unit cell with lattice parameters: a = 7.260 Å, b = 2.950 Å, c = 5.117 Å and β = 103.7°. A Rietveld analysis shows that this compound has a layered structure based on CrO2 sheets consisting of edge-shared CrO6 octahedra. Such a layered structure is commonly seen in many hexagonal Cr oxides such as NaCrO2. A heat treatment at 100 °C modifies the crystal structure without destruction of a layered structure based on Cr triangular-lattice, because H2O molecules among the CrO2 sheets are removed at high temperature. Magnetization measurements reveal a spin-glass behavior below Tg = 3 K.

Abstract: Band structure calculations for EuCo2X2 (X = Si, Ge) and EuM5¬ (M = Ni, Cu) were performed using FP-LAPW and FPLO DFT codes. Correlations were taken into account within Around Mean Field (AMF) and Fully Localized Limit (FLL) approaches. Antiferromagnetic supercell was constructed for EuCo2X2. Several exchange-correlation potentials were used for EuM5. Equilibrium lattice parameters were calculated for EuM5 and used to study the magnetic properties. Calculated europium valence is between 2.3 and 2.5 and slightly higher for EuNi5 and EuCo2Si2 than for EuCu5 and EuCo2Ge2. LSDA+U calculations within the AMF double-counting scheme are in better agreement with photoemission data than calculations using the FLL approach.