Study of Valence Band O2p–Subzone Structure of Rare Earth Tantalates and Similar Substances by X-ray Spectroscopy Method

Abstract

The objects of this investigation were tantalates LnTaO 4 (Ln La Lu), niobate LaNbO 4 , and oxides Ta 2 O 5 , Nb 2 O 5 , La 2 O 3 . The LaTaO 4 ortorhombic modification manufactured by the authors possesses of high thermostability and has the polar space group (SG) Cmc2 1 . The NdTaO 4 modification with a structure like monocline LaTaO 4 (a high pressure phase HPP) was also manufactured. This phase and other LnTaO 4 phases are base of luminescent materials. In LaNbO 4 the phase transition from M-fergusonite modification to one with ferroelectric BaMnF 4 structure and SG Cmc2 1 was realised first in our work through treating the initial modification by heating and high pressure.The oxygen X-ray spectra OKα were obtained for all above mentioned compounds. The spectra show that oxygen p-electrons form a subzone of the width about 6-7 eV in the valence zone. The changes of the Ln4f-electron quantity in isostructural LnTaO 4 rows influence poorly O2p-distribution shape. The phase transition in NdTaO 4 and LaNbO 4 also influences poorly O2p-subzone structure. The similarity of the O2p-subzone structure was observed for the isostructural LaNbO 4 and LaTaO 4 . The genesis of tantalates and LaNbO 4 O2p-subzone structure was revealed.