MVO4-Ta2O5-Nb2O5 (M = Y, La) solid solutions

The subsolidus phase relations in the MVO₄-Ta₂O₅-Nb₂O₅ (M = Y, La) systems were studied. MNb_2-2xTa_2xVO₉ (I) and MTa_2-2xNb_2xVO₉ (II) solid solutions were prepared and characterized by x-ray diffraction, vibrational spectroscopy, and electron spin resonance. The range of solid solutions in I isx = 0–0.58 for M = Y and 0–0.4 for M = La; in II,x = 0–0.09 for M = Y and 0–0.1 for M = La. All of the solid solutions were found to contain V(IV) centers whose nearest neighbor environment depended on composition. The structure of LaTa_2-2xNb_2xVO₉ was shown to contain fragments characteristic of LaNb₂VO₉. The lattice parameters of these solid solutions correlate with the V(IV) content.     

Quasi-One-Dimensional Natures in (Et n Me4−n Z)[Pd(dmit)2]2

We studied one of possible ground states for Pd(dmit) ₂ salts in a dimerized two-band Hubbard model. By using a strong-coupling expansion, we obtained an effective dimer model which has a quasi-one-dimensional Fermi surface. In the insulating phase, it leads to the Heisenberg model on an anisotropic triangular lattice. We calculated effective exchange coupling strengths within the second order perturbation theory and found that both ferromagnetic and antiferromagnetic couplings are possible. Similarities to and differences from Ni(dmit) ₂ salts are discussed.     

Crystal Structure of K[UO2(NO3)3] and Some Features of Compounds M[UO2(NO3)3] (M = K,Rb, and Cs)

Greenish-yellow transparent crystals of K[UO₂(NO₃)₃] were prepared from aqueous solutions as by-product in synthesis of potassium chromatouranylates. The crystal structure was solved by the direct methods and refined to R ₁ = 0.037 (wR ₂ = 0.070) for 1452 reflections with |F _hkl| 4|F _hkl|. Mono- clinic system, space group C2/c, a = 13.4877(10), b = 9.5843(7), c = 7.9564(6) Å, = 116.124(2)°, V = 923.45(12) ų. The structure of K[UO₂(NO₃)₃] contains isolated complex ions [UO₂(NO₃)₃]^- whose uranyl groups are aligned parallel to the [-101] plane. The K⁺ cations, coordinated by twelve oxygen atoms, are located between the complex anions. Comparison of the structure with known data on M[UO₂(NO₃)₃] compounds (M = K, Rb, Cs) suggests the possibility of phase transitions due to relatively small displacements of [UO₂(NO₃)₃]^- anions and K⁺ cations, retaining the general structural motif.     

Maximum-girth slope-based quasi-cyclic (2, k ⩾ 5) low-density parity-check codes

A class of maximum-girth geometrically structured regular (n, 2, k ⩾ 5) (column-weight 2 and rowweight k) quasi-cyclic low-density parity-check (LDPC) codes is presented. The method is based on cylinder graphs and the slope concept. It is shown that the maximum girth achieved by these codes is 12. A lowcomplexity algorithm producing all such maximum-girth LDPC codes is given. The shortest constructed code has a length of 105. The minimum length n of a regular (2, k) LDPC code with girth g ? 12 determined by the Gallager bound has been achieved by the constructed codes. From the perspective of performance these codes outperform the column-weight 2 LDPC codes constructed by the previously reported methods. These codes can be encoded using an erasure decoding process.     

Heat Capacity and Thermodynamic Functions of NdMeFe2O5 (Me is Li, Na, K, Cs) Ferrites

The values of heat capacity of NdMeFe₂O₅ (Me is Li, Na, K, Cs) ferrites in the temperature range from 298 to 673 K are experimentally determined. Equations of the temperature dependence of heat capacity are derived and used to calculate the thermodynamic functions C _p ⁰(T), S ⁰(T), H ⁰(T) - H ⁰ (298.15 K), and **(T) of ferrites in the range identified above.     

Infrared and raman investigations of the charge ordering phenomena in the monoclinic salts κ-(BEDT-TTF)4[M(CN)6][N(C2H5)4]·2H2O (M=CoIII, FeIII)

The monoclinic crystals of κ-phase charge-transfer salts formed by BEDT-TTF with Co(CN)₆ or Fe(CN)₆ anions undergo a phase transition at T=150 K. Temperature dependences of FT-NIR Raman spectra and IR reflectance spectra were studied. We show that the phase transition is related to a charge ordering and there exist charge fluctuations above 150 K.     

Infrared and Raman Investigations of the Charge Ordering Phenomena in the Monoclinic Salts κ-(BEDT-TTF)4[M(CN)6][N(C2H5)4]·2H2O (M = CoIII, FeIII)

The monoclinic crystals of κ-phase charge-transfer salts formed by BEDT-TTF with Co(CN)₆ or Fe(CN)₆ anions undergo a phase transition at T = 150 K. Temperature dependences of FT-NIR Raman spectra and IR reflectance spectra were studied. We show that the phase transition is related to a charge ordering and there exist charge fluctuations above 150 K.