Crystallography and properties of La2WO6 lanthanum oxytungstate

Crystallographic, optical and dielectric characteristics of the lanthanum oxywolframium crystals, produced by crystallization from the melt solution, was investigated. Chemical composition of the crystals can be represented by the formulae: Lasub(2)Wsub(1+x)Osub(6+3x) and corresponds to the solid solution of WO3 in La2WO6. By its crystallographic characteristics lanthanum oxywolframium significantly differs from the other compounds of wolframium and molybdenum with rare earth elements Re2W(Mo)O6 type. La2WO6 crystals belong to the hexogonal singony and they have laminated structure, which determines their polytype. The most spreaded hexalayer polytype has pr.gr. P63/mmc and the elementary cell parameters are: a=9,04+-0,01 A; c=6 C0=32,60-33,65 A depending on the crystal composition. Frequently penta- and heptalayer polytypes are found. Crystals are transparent in the visible spectra region, have one optical axis and high refraction index