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Information × Registration Number 0201U003660, 0100U003284 , R & D reports Title Optical, thermal and magnetic properties of systems with mesoscopic spatial nonuniformities popup.stage_title Head Popkov Yu.A., Registration Date 03-04-2001 Organization Kharkov National University named after V.N. Karazin popup.description2 The results of investigation of Raman spectra in the region of intrinsic vibrations of the ammonium ions in mixed K1-x(NH4)xH2PO4 crystals with various ammonium concentrations (х = 0.22; 0.32; 0.53; 0.74; 0.82) are considered in the temperature range 4.2-300K. The analysis of the frequency and half-width temperature dependencies confirms the fact that the ammonium ions positions in the crystals lattice is not fixed in the paraelectric phase. The ammonium ions make jumps involving a change in the positions of center of mass. The activation energies of these reorientation processes are determined. It has been revealed that at the temperatures of the order of 110-120K the correlated fixation of the ammonium ions in the lattice occurs for all K1-x(NH4)xH2PO4 crystals irrespective of the ammonium concentration. Fixation of the ammonium ions gives rise to the antiferroelectric cluster structure formations. For crystals with concentrations х = 0.22; 0.32; 0.53 such structure is preserved down to helium tem perature in the structural glass phase, but for crystals with х = 0.74; 0.82 — down to antiferroelectric phase transition temperatures Tn (68,5 and 80,5 respectively). The similar processes in isostructural crystal Rb0.20(NH4)0.80Y2PO4 have been found. Product Description popup.authors popup.nrat_date 2020-04-02 Close