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  • Dielectric and polarization properties of SrTiO3-based quantum paraelectrics

    The doelectric and polarization studies of the system of solid solutions PbxSr1-xTiO3 with x = 0.005, 0.02, 0.04 in a broad frequency and temperature range are performed. The temperature of the ferroelectric phase transition in the solid solutions is determined. The temperature behaviour of the remanent polarization at the phase transition is established.

    Keywords: quantum paraelectric, strontium titanate, dielectric permittivity, remanent poalrization, superparaelectric state, phase transition

  • Temperature dependence of the two-magnon excitations in Nd-doped bismuth ferrite films

    High-temperature (295 - 1000 K) Raman studies of Nd-doped bismuth ferrite epitaxial heterostructures were performed. The bands 620 cм-1 and 1260 cm-1 were observed in the high-frequency range above the first-order phonons. The band 620 cм-1 corresponds to the maximum density of states of magnon branch at the Brillouin zone boundary. The intense second-order band at about 1260 cm-1 corresponds to the density of states of two-magnon excitations. The intensity of two-magnon scattering decreases with increasing temperature, and above the Neel temperature paramagnon scattering typical for antiferromagnetics was observed.

    Keywords: Raman spectroscopy, multiferroic, bismuth ferrite, heterostructure

  • Methods for the synthesis of LaMnO3 (Review)

    "This review covers various methods of synthesis LaMnO3 ferroics. The general analysis of the solid-phase synthesis reactions methods and wet methods (sol-gel, sorption, co-precipitation) are carred out. The original results of LaMnO3 syntheses from various precursors by means of the in situ method are showned. The advantages and disadvantages of different methods of synthesis are determined. The analysis of synthesis LaMnO3 ferroics published data is shown:
    - the structure formation of LaMnO3 in perovskite-type phases occurs at different temperatures, depending on precursors states;
    - LaMnO3 perovskite phases differ in symmetry and unit cells parameters at room temperature, depending on the preparation conditions;
    - the highest synthesis temperature of LaMnO3 are typical for solid phase reactions method (950-1050 ° C), the lowest - for wet synthesis methods (500-700 ° C);
     - the synthesis conditions effect the stoichiometry of LaMnO3 for oxygen content.
    Our studies of structure formation processes of LaMnO3 by in situ method are allowed to define the role of precursors states at synthesis of solid phase reactions methods, adsorption, co-precipitation and sol-gel mixtures.
    It is determined that in samples prepared by wet chemical methods, the formation processes of  LaMnO3 perovskite phases occur at lower temperatures than by solid phase reaction (sol-gel precursor - 500 <T <600 ° C; precursors obtained by coprecipitation and sorption methods - at 600 <T <700 ° C and 700 <T <800 ° C, respectively).  

    Keywords: ferroics, LaMnO3, X-ray diffraction, solid-phase synthesis, sol-gel synthesis, sorption, co-precipitation