Перегляд за Автор "Kolomoets, Anna"

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  • Ескіз
    Документ
    Dielectric properties of the low-temperature phase transitions in divalent nitrates
    (Sumy State University, 2023) Kolomoets, Anna
    The paper is devoted to the elucidation of realization mechanism of the low-temperature phase transitions in divalent nitrates Pb(NO3)2, Sr(NO3)2 and Ba(NO3)2. The investigations results of dielectric permeance ε and tangent of dielectric losses angle tgδ temperature dependencies are presented for lead nitrate Pb(NO3)2. The investigations confirm supposition that low-temperature phase transitions in divalent nitrates occurs because of “freezing” of reorientational oscillations of NO3− groups around Nitrogen atom, which occur at room temperature. A maximum in Pm3→P213 phase transition region is observed on the ε(T) curves. This maximum decreases with increasing of frequency and at 10KHz frequency becomes like a “step” by it’s form. Two maximums are observed on the tgδ(T) curves. First of them occurs at the phase transition temperature, another one is moved to low-temperature region. The conclusion, that the first maximum of tgδ is connected with NO3− groups relaxation and second maximum is connected with a formation of domain structure is made. The energy of activation is calculated by the removing of dielectric permeance maximum and this energy is higher than 2 eV. Such value of activation energy is proper for heavy ions. This fact confirms a supposition, that a relaxation of NO3− groups occur at 1KHz – 10KHz frequencies in the phase transition region.
  • Ескіз
    Документ
    Searching for Order Parameter of Low-temperature Phase Transitions in Divalent Nitrates
    (Journal of Nano- and Electronic Physics, 2019) Kolomoets, Anna; Khrypko, Sergiy
    The paper is devoted to the searching for order parameter of low-temperature phase transitions in divalent nitrates Pb(NO3)2, Sr(NO3)2 and Ba(NO3)2. According to the curves of temperature dependencies χ14 component of the tensor quadratic susceptibility the conclusion is made that the low-temperature phase transitions in divalent nitrates are the phase transitions of the first order with the features of the second order. The mechanisms of the low-temperature phase transitions in divalent nitrates are discussed from this perspective.