THE PECULIARITIES OF GLASS STATE FORMATION AND THE ROLE OF RANDOM ELASTIC FIELDS IN MIXED-CRYSTALS OF THE KH2PO4 FAMILY

The source of random static electrical fields, which is determined by both the piezoelectric coupling and the static elastic deformations induced by substitutional disorder of ions with different ionic radii has been considered for mixed crystals of the KH2PO4 family. It is shown that the random electrical fields act mainly on the lattice polarization along the c axis and up-down proton configurations. The short-range interactions of four acid protons surrounding a PO4 group are represented as the random local uniaxial anisotropy for the mixed crystals provided the ice rule condition is fulfilled. It is also shown that the distinction of symmetry between the up-down and lateral proton configuration, and the peculiarities of proton-lattice interaction can lead to the coexistence of long-range order (for up-down/lateral configuration) with the glass or paraelectric (for lateral/up-down configuration) state.