Crystal structures and structural relationships of KFe2(SeO2OH)(SeO3)3 and SrCo2(SeO2OH)2(SeO3)2

The new phases KFe₂(SeO₂OH)(SeO₃)₃ and SrCo₂(SeO₂OH)₂(SeO₃)₂ have been synthesized under low-hydrothermal conditions and their structures were determined by single-crystal X-ray methods. Both compounds are monoclinic; KFe₂(SeO₂OH)(SeO₃)₃: space group P2, A = 9.983(4), B = 5.270(1), C = 10.614(4) Å, β = 97.42(2)°, V = 553.7 ų, Z = 2; SrCo₂(SeO₂OH)₂(SeO₃)₂: space group P2ln, A = 14.984(2), B = 5.286(1), C = 13.790(2) Å, β = 94.72(1)°, V = 1088.5 ų , Z = 4. The refinements converged to R-values of 2.9 and 3.6% respectively.

The atomic arrangement in KFe₂(SeO₂OH)(SeO₃)₃ and SrCo₂(SeO₂OH)₂(SeO₃)₂ is based on isolated MO₆ octahedra (M = Fe³⁺, Co²⁺), which are corner-linked via trigonal pyramidal selenite groups to a framework structure. Interstitials are occupied by potassium or strontium atoms in ten- or eight-coordination respectively, and by the lone-pair electrons of the Se⁴⁺ atoms. Both compounds are not isotypic but are closely related and may be interpreted as different distortions of an idealized structure type in space group P2/m, which was modelled for a theoretical compound SrFe₂(SeO₃)₄ by distance least squares refinement (program ).     

STM spectroscopy in superconducting phase of (BEDT-TTF)2Cu(NCS)2

The superconducting phase of (BEDT-TTF)₂Cu(NCS)₂ was investigated with use of the scanning tunneling microscope (STM).The tunneling conductance was measured at the b-c surface of a single crystal. The differential conductance shows a clear superconducting gap structure below the transition temperature and its value is reduced to almost zero around zero bias voltage at 1.9 K. The conductance curve is not well fitted to the BCS one but suggests the gap anisotropy. However, the gap with line nodes, expected from the simple d-wave symmetry, is excluded. Possible models for the superconducting gap are as follows; (1) the gap with point nodes or (2) the anisotropic gap with a minimum value Δ_min1 mev. It is understood that the superconducting gap is highly anisotropic in k-space.     

Fermi surface reconstruction in (BEDT-TTF)2TlHg(SCN)4

The Shubnikov-de Haas (SdH) measurements of the two dimensional organic conductor (BEDT-TTF)₂TlHg(SCN)₄ have been performed to investigate the Fermi surface reconstructed by the spin density wave formation. At 0.05 K, ten different SdH oscillations are found. A model of the reconstructed Fermi surface is proposed on the basis of the relation between the observed SdH frequencies.     

ESR study of the phase transitions in organic conductors (H8-ET)2[Hg(SCN)2Br] and (D8-ET)2[Hg(SCN)2Br]

A significant effect of the deuteration on the ESR parameters of the investigated compounds is described. The differences in the physical properties of these salts are attributed to an enhancement of the dimerization in the cationic sheets caused by the hydrogen bond and the anion-cation interaction in hydrogenated salt at low temperatures.     

Low-frequency Raman spectra in κ-(BEDT-TTF)2Cu(NCS)2 and κ-(BEDT-TTF)2Cu[N(CN)2]Br

The ordering of the terminal ethylene groups of the BEDT-TTF molecule, i.e., the staggered or eclipsed conformation, in κ-(BEDT-TTF)₂Cu(NCS)₂ and κ-(BEDT-TTF)₂Cu[N(CN)₂]Br was studied between 18 and 295 K by Raman scattering. The low-frequency spectra of these compounds are similar to each other. Broad peaks at about 55 cm⁻¹ extremely broadened and their intensities became weak with decreasing temperature. The anomalous behaviour was interpreted in terms of critical dynamics of the pseudospin-phonon coupled system, where the spin states represent the conformations of the terminal ethylene groups. It was found that the ordered state is formed around the superconducting critical temperature.     

Anisotropic superconductivity in κ-(BEDT-TTF)2Cu(NCS)2

To determine the symmetry of the superconducting energy gap, we measured the ac-susceptibility of κ-(BEDT-TTF)₂Cu(NCS)₂. With shielding geomagnetic field, we confirmed the power law temperature dependence of magnetic-field penetration depth. This result indicates an anisotropic superconductivity of gapless nature in this system. The penetration depth extrapolated to 0K for parallel field was found to be 0.22mm of macroscopic size.     

Dielectric and piezoelectric properties of Sb doped (NaBi)0.38(LiCe)0.05[]0.14Bi2Nb2O9 ceramics

Sb⁵⁺-doped (NaBi)_0.38(LiCe)_0.05[]_0.14Bi₂Nb₂O₉ (represented as NBNLCS-x, where [] represents A-site vacancies) ceramics were prepared by the conventional solid-state route. The ceramics well sintered to approach ∼98.5% theoretical density and the tetragonality of crystal structure increased with Sb⁵⁺ additions. However, the Curie temperature (T_C) and the piezoelectric coefficient (d₃₃) of Sb⁵⁺-modified ceramics gradually decreased. The 3 mol% Sb⁵⁺-doped samples exhibited optimum properties with a d₃₃ value of ∼22 pC/N planar electromechanical coupling factor (k_p) of ∼11.2% and relatively high T_C of ∼765 °C. These results indicate that NBNLCS-x material is a promising candidate for high-temperature piezoelectric applications.     

Thermal expansion studies on Th(MoO4)2, Na2Th(MoO4)3 and Na4Th(MoO4)4

Thermal expansion behavior of Th(MoO₄)₂, Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ was studied under vacuum in the temperature range of 298–1123 K by high temperature X-ray diffractometer. Th(MoO₄)₂ was synthesized by reacting ThO₂ with 2 mol of MoO₃, at 1073 K in air and Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were prepared by reacting Th(MoO₄)₂ with 1 and 2 mol of Na₂MoO₄, respectively at 873 K in air. The XRD data of Th(MoO₄)₂ was indexed on orthorhombic system where as XRD data of Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were indexed on tetragonal system. The lattice parameters and cell volume of all the three compounds, fit into polynomial expression with respect to temperature, showed positive thermal expansion (PTE) up to 1123 K. The average value of thermal expansion coefficients for Th(MoO₄)₂, Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were determined from the high temperature data.     

Optical study of praseodymium dicarboxylate [Pr(H2O)]2[O2C(CH2)3CO2]3.4H2O

Praseodymium dicarboxylate, [Pr(H₂O)]₂[O₂C(CH₂)₃CO₂]₃.4H₂O]–glutarate, Pr[glut], is synthesized by hydrothermal techniques. The title compound crystallizes in the monoclinic space group C2/c (No. 15). The rare earth cation is coordinated by nine oxygen atoms, eight oxygen atoms from the carboxylate groups and one from the water molecule. The local symmetry of Pr site is low, C_s. The absorption spectra of Pr[glut] are recorded from the visible to the far IR domain at 300, 77 and 9 K. Under various Ar⁺ laser excitations no emission is detected from ³P₀ and ¹D₂ excited levels of Pr³⁺ ion. In the low temperature absorption spectra only one electronic line is recorded for ³H₄→³P₀ transition. It confirms a unique local environment for the rare earth ion in Pr[glut]. The utility of the ‘barycenter curves’ in the attribution of electronic lines is demonstrated. Energy level scheme of 36 Stark components is deduced from the absorption spectra. The parametric calculation was performed on the whole 4f² (Pr³⁺) configuration with the starting set of crystal field parameters obtained previously for the Eu³⁺ ion in the isostructural compound. Eight free ion and nine phenomenological crystal field parameters in C_2v symmetry reproduce quite well several electronic levels of Pr³⁺ ion experimentally observed in Pr[glut]. A good r.m.s. standard deviation of 14.8 cm⁻¹ is obtained.     

Electrochemical performances of Ag–(Bi2O3)0.75(Y2O3)0.25 composite cathodes

The electrochemical performances of Ag–Y_0.25Bi_0.75O_1.5 (YSB) composite cathodes on Ce_0.8Sm_0.2O_1.9 (SDC) electrolytes have been investigated at intermediate temperature using AC impedance spectroscopy. The results indicated that the electrochemical performances of these composites are quite sensitive to the compositions and the microstructures of the cathode. The optimum YSB addition to Ag resulted in 10 times lower area specific resistance. The ASR of Ag-50 vol.% YSB was about 0.12 Ωcm² at 700 °C as compared to 3.9 Ωcm² for Ag cathodes. The observed high performance of Ag–YSB composite cathodes might be due to the high oxygen-ion conductivity of YSB and its high catalytic activity for oxygen reduction.     

Magnetoresistance anisotropy in the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2

We report on systematic studies of the magnetoresistance (MR) anisotropy of κ-(BEDT-TTF)₂Cu(NCS)₂ at ambient pressure and at P = 1.2 kbar. Prominent oscillations of the interplane MR are found under magnetic field rotating in various planes normal to the 2D bc-plane. The oscillations are mainly associated with the existence of the open Fermi surface along the K_aK_c-plane, revealing however somewhat complicated behaviour which is most likely due to the specifics of multiply connected Fermi surface.     

Thermodynamic analysis on reaction behaviors of silicates in (NH4)2WO4-(NH4)2CO3-NH3-H2O system

The reaction behaviors of silicate species in (NH₄)₂WO₄-(NH₄)₂CO₃-NH₃-H₂O system are crucial to developing a green manufacture technique for ammonium paratungstate. In order to efficiently remove silicon from the system, the reaction behaviors of silicate species were systematically investigated by thermodynamic analysis. The thermodynamic analysis shows that silicate in the tungstate clinker partly decomposes in the leaching process, with 150–160 mg/L silicon thermodynamically at 25 °C. The dissolved silicon can be removed by magnesium salts via forming insoluble MgSiO₃. The low carbonate and high ammonia concentrations in the system are beneficial to the removal of silicon, with silicon concentration reaching 8–10 mg/L thermodynamically, whereas MgSiO₃ precipitation is hardly formed when the concentration of total carbonate is more than 1.5 mol/L. The reaction behaviors of calcium and magnesium were also studied in the system. The results in the verification experiments consist with the theoretical calculation.     

Electronic properties of the organic superconductor (BEDO-TTF)2ReO4(H2O)

The electronic properties of the organic superconductor (BEDO-TTF)₂ReO₄(H₂O) were investigated by temperature dependent resistivity, FT - IR reflectivity and magnetoresistance measurements. Shubnikov-de Haas (SdH) oscillations were observed in magnetic fields up to 24T in the temperature range from 0.5K to 4.2K. The two observed SdH frequencies of 76 and 37 Tesla correspond very well to two cross-sectional areas of the Fermi surface obtained from a tight binding calculation for a hole and an electron pocket.