Structure and influence of pressure on low-temperature dielectric properties of nanocomposites based on mesoporous glasses containing K$_{(1-x)}$(NH$_4$)$_x$H$_2$PO$_4$

The results of a study of the structure and influence of pressure on the dielectric response of nanocomposite materials based on mesoporous glass with an average pore diameter of 7(2) nm containing solid solutions of K$_{(1-x)}$(NH$_4$)$_x$H$_2$PO$_4$ introduced into the pore space are presented with $x$ = 0.05, 0.1 and 0.15. It is shown that in nanocomposites with $x$ = 0.1 and 0.15 tetragonal and monoclinic phases coexist. For the composition with $x$ = 0.05, the phase diagram $T_C(P)$ was obtained and the coefficient $dT_C/dP\approx$ -2.5(2) was determined. In nanocomposites with $x$ = 0.05 and 0.15 at $P$ = 0, an increase in the ferroelectric phase transition temperature $(T_C)$ is observed compared to similar bulk materials.