a), M. A. BUNIN (a), 3%. A. BLOKHIN (a), V. I. MIXW (b), V. D. PROCHUKHAX (c), and G. K. AVERKIEVA (c) K-bands and absorption spectra of phosphorus and emission Le, 3-bands of silicon and phosphorusin MgSiP,, ZnSiP,, and CdSiP, are obtained. From a comparison of the spectra of different series and components in these compounds the influence of metal d-states on the valence band structure is studied. The admixture of phosphorus and zinc states to a metal d-state is estimated from the ZnSiP, spectra. Its smallness and the similarity of shape, position, and relative intensity of details of the corresponding spectra of all compounds are indicative of the fact that all metal d-states are only slightly hybridized with other states and only weakly affect the valence band structure. A sufficiently fair correspondence is revealed between the calculated spatial charge density distribution of valence electrons and the data about the localization and symmetry of electron states obtained from X-ray spectra. Good agreement between A E and E , is found ( A E is the energy gap between the emission ending and the onset of absorption of corrected P K-spectra, E , is the energy gap obtained by other physical methods). nOJIyYeHb1 K-nonocbI M CneKTpbI IIOrJIOJ.UeHMfi @OC@Opa, a TaHWe 3HMCCMOHHbIe Lz, 3-CneKTpOB pa3JIWlHbIX CepMfi M KOMnOHeHTOB 3 T M X COeEMHeHMfi II03BOJIHJlO MCCJIeXOBZiTb l) Prospekt Stilckki 192, 341090 Rostov-on-Don, USSR. 49 physica (b) loo/?

E l e c t r o n i c Structure of A g N b 0 3 : X -R a y E m i s s i o n and X A N E S Study

- Institute of Physics, Rostov State University 1) (a) andSbSI is the most studied compound of V-VI-VII type owing to the coexistence of strong ferroelectric and semiconductor properties. The data on i t s isotype SbSeI and their solid solutions a r e insufficient although investigations of such compounds are of particular interest. The phase transition point in SbSxSel-xI exhibits a nearly linear dependence on temperature when 0.3 2 x 1 and does not occur when x < 0.3. The forbidden gap in this system decreases monotonously with increasing selenium content /1, 2/. So it is possible to obtain single crystals of mixed compounds with electrophysical properties dependent on the ratio of the initial components. In particular, one can synthesize crystals possessing a fixed point of phase transition and width of the forbidden gap. To carry out such purposeful synthesis and to extrapolate the revealed regularities on a wider class of objects it is reasonable to investigate the character of the electron subsystem behaviour when the sulphur/selenium ratio in solution varies. The aim of this note is an X-ray analysis of changes in the electron state distribution when sulphur i s substituted by selenium.In the present note for the first time there are obtained X-ray fluorescent sulphur K-bands in SbSxSel-xI (x = l , O , 0.7, 0.25). The technique for obtaining spectra is described in /3/. A scheme for constructing energy bands in SbSI was proposed earlier /4/. It w a s developed on the basis of a comparison of X-ray data with calculations reported in/5/.Generally, the structure of the SK-band in SbS Sel-xI is similar to that of X SbSI (Fig. 1). This fact suggests an identical nature of the nearest surrounding of sulphur atoms in these compounds. Really, the Lattice symmetry remains unchanged when sulphur atoms are partially replaced by selenium ones /2/. 1) prospekt Stachki 194, 344090 Rostov-on-Don, USSR.2) 39 Studentu, 232034 Vilnius, USSR.

The X-ray emission K and L2,3 bands of sulphur and phosphorus as well as their X-ray K absorption spectra are obtained for the semiconductors TlAsS2, Tl3AsS3, Tl3AsS4, Tl3PS4 and Tl3TaS4. The upper part of the valence band in the compounds investigated is formed of the S p states mainly, but the S s states are localized near the bottom of the valence band and hardly take part in the bonding. Comparison of the X-ray spectra of S and P in the isoelectronic and isostructural compounds Tl3AsS4 and Tl3PS4 has made it possible to determine the energy position of the p states of arsenic in Tl3AsS4. The energy distributions of the valence electron states of sulphur and its neighbours in all the compounds investigated are analysed and the covalent-ionic mechanism of chemical bonding is proposed.

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