Synthesis and study of cesium-containing phosphates with a β-tridymite structure

Complex phosphates CsMg_{1 ? x} M _x PO₄ (M = Mn, Co, Cu, Zn), containing cesium and metals in the oxidation state +2, have been synthesized, and their structure and thermal behavior have been studied. Continuous solid solutions (0 ?? x ?? 1) of the ??-tridymite structure type are formed in the CsMg_{1 ? x} Mn _x PO₄, CsMg_{1 ? x} Co _x PO₄, and CsMg_{1 ? x} Zn _x PO₄ systems, whereas limited solid solutions (0 ?? x ?? 0.4) are formed in the CsMg_{1 ? x} Cu _x PO₄ system. Based on DTA data, phase transitions have been revealed in the cobalt-, copper-, and zinc-containing phosphates, and the orthorhombic or monoclinic crystal system has been identified. Unit cell parameters of the solid solutions have been calculated. Thermal expansion of the CsMPO₄ phosphates has been studied.     

Local structure of divalent silver complexes in fluorite crystals as seen by EPR method

The analytical expressions for spin-Hamiltonian parameters of Jahn-Teller paramagnetic centres [AgF₂F₆]^6? in fluorite crystals are deduced. Comparison with the experimental EPR data for CdF₂, CaF₂ and SrF₂ yields information about the local structure of centres [AgF₂F₆]^6?. It is found that two Ag²⁺-F^? bonds of the centre (along the 〈111〉 direction) are shorter than the rest six bonds by factor 1.1. Euler angles of six non-axial fluorines are almost the same as those in the undistorted fluorite structure.     

EPR of trivalent chromium centers with monoclinic symmetry in SrF2 crystals

Cr³⁺ centers with monoclinic symmetry in SrF₂:Cr crystals are studied by EPR. Based on an analysis of the EPR data and a study of the conditions under which the observed samples were formed, a model is proposed which explains the low symmetry of the magnetic properties in terms of the simultaneous effect on the impurity ion state of interactions with the interstitial F⁻ ion and with normal vibrations of the crystal lattice in a trigonal symmetry. Fiz. Tverd. Tela (St. Petersburg) 39, 302–305 (February 1997)     

Heteronuclear coordination compounds of copper and cobalt in urethane-yielding reactions

Heteronuclear coordination compounds capable of catalyzing the low-temperature dissociation of urethane groups were synthesized on the basis of copper and cobalt chlorides. The study was performed with an urethane prepolymer produced from oligoester diol and 2,4-toluylene diisocyanate. It was found that the dissociation of urethane groups in the prepolymer is accompanied by formation of carbodiimides and release of 2,4-toluylene diisocyanate. As a result of the subsequent redox interaction, Cu(II) ions are mostly converted to Cu(I), and the involvement of isocyanate groups in the para-position into the reaction processes leads to formation of azoaromatic derivatives. It is shown that their coordination binding by Co(II) ions strongly affects both the supramolecular organization of polyurethanes and a set of their physicomechanical properties.     

Three-Pulse ELDOR Theory Revisited

The current theory of three-pulse electron double resonance (PELDOR) has been generalized to the case, when paramagnetic particles (spin labels) in pairs or groups have the electron paramagnetic resonance (EPR) spectra, which overlap essentially or coincide. The PELDOR signal modulation induced by the dipole–dipole interaction between paramagnetic spin ½ particles in pairs embedded in disordered systems has been analyzed comprehensively. It has been shown that the PELDOR signal contains additional terms in contrast to the situation considered in the current theory, when the EPR spectra of the spin labels in the pairs do not overlap. In disordered systems, the pairs of spin labels have the characteristic dipolar interaction frequency. According to the current theory for pairs of spin labels, the PELDOR signal reveals the modulation with this characteristic frequency. The additional terms, which are obtained in this work, do not change the modulation frequency of the PELDOR signal for pairs of spin labels. However, these additional terms should be taken into account when analyzing the amplitude of the PELDOR signal and the amplitude of the modulation of the PELDOR signal. The consistent approach to treating the PELDOR data for the groups containing three or more spin labels has been outlined on the basis of the results for pairs of spin labels. It has been also analyzed how the spin flips and molecular motion or molecular isomerization can affect the manifestation of the interaction between the spin labels in PELDOR experiments. PELDOR experiments for the stable biradicals (biradicals I containing 1-oxyl-2,2,5,5-tetramethylpyrroline-3-yl spin labels and biradicals II containing 3-imidazoline spin labels) have been performed. The results have been interpreted within the theory developed in this work.     

Entropy Group in Parastatistics of Quantum Nonextensive Systems

Russian Physics Journal - An Abelian group of entropies is defined and its representations for quantum nonextensive systems with a composition law having quadratic nonlinearity are determined. Its...