Study of phase transformations in (Cs,NH$_{4}$)$_{4}$(HSO$_{4})_{3}$(H$_{2}$PO$_{4}$) crystals

Phase transitions in crystals of (Cs,NH$_{4})_{4}$(HSO$_{4}$)$_{3}$(H$_{2}$PO$_{4}$) solid solutions have been investigated by synchronous thermal analysis and polarization microscopy at different temperatures. The temperatures of structural modifications are established; it is shown that the replacement of Cs cations with NH$_4$ in Cs$_{4}$(HSO$_{4})_{3}$(H$_{2}$PO$_{4}$) crystals reduces the temperatures of phase transformations.