No abstract

No abstract

No abstract

Four new manganese germanates and silicates, AMnGeO (A = Li, Na) and AMnSiO (A = Na, Ag), were prepared, and their crystal structures were determined using the X-ray Rietveld method. All of them contain all components in tetrahedral coordination. LiMnGeO is orthorhombic (Pmn2) layered, isostructural with LiCdGeO, and the three other compounds are monoclinic (Pn) cristobalite-related frameworks. As in other stuffed cristobalites of various symmetry (Pn AMXO, Pna2 and Pbca AMO), average bond angles on bridging oxygens (here, Mn-O-X) increase with increasing A/X and/or A/M radius ratios, indicating the trend to the ideal cubic (Fd3̅m) structure typified by CsAlO. The sublattices of the magnetic Mn ions in both structure types under study (Pmn2 and Pn) are essentially the same; namely, they are pseudocubic eutaxy with 12 nearest neighbors. The magnetic properties of the four new phases plus LiMnSiO were characterized by carrying out magnetic susceptibility, specific heat, magnetization, and electron spin resonance measurements and also by performing energy-mapping analysis to evaluate their spin exchange constants. AgMnSiO remains paramagnetic down to 2 K, but AMnXO (A = Li, Na; X = Si, Ge) undergo a three-dimensional antiferromagnetic ordering. All five phases exhibit short-range AFM ordering correlations, hence showing them to be low-dimensional magnets and a magnetic field induced spin-reorientation transition at T < T for all AFM phases. We constructed the magnetic phase diagrams for AMnXO (A = Li, Na; X = Si, Ge) on the basis of the thermodynamic data in magnetic fields up to 9 T. The magnetic properties of all five phases experimentally determined are well explained by their spin exchange constants evaluated by performing energy-mapping analysis.

Equilibria E 4000 Crystal Structure, Phase Relations and Electrochemical Properties of Monoclinic Li 2 MnSiO 4 . -Phase relations in the MnO-SiO 2 -Li 4 SiO 4 subsystem are characterized by powder XRD after solid state reactions in hydrogen at 950-1150°C. Li2MnSiO4, existing in the system, crystallizes in the monoclinic space group P21/n with Z = 4, and is isostructural with γII-Li2ZnSiO4 and low-temperature Li2MgSiO4. Only 4% Li can be extracted from Li2MnSiO4 in an electrochemical cell between 3.5 and 5 V against Li metal. Neither the orthorhombic nor the monoclinic modification of Li2MnSiO4 is suitable for battery applications. -(POLITAEV, V. V.; PETRENKO*, A. A.; NALBANDYAN, V. B.; MEDVEDEV, B. S.; SHVETSOVA, E. S.; J. Solid State Chem. 180 (2007) 3, 1045-1050; Fac. Chem., Rostov State Univ., Rostov-on-Don 344090, Russia; Eng.) -W. Pewestorf 52-016