Transmission electron microscopy study of KDP crystals

Abstract

KDP crystals were examined by transmission electron microscopy (TEM). Transmission electron diffraction (TED) patterns and images of some crystal areas indicated the existence of the second orthorhombic phase in tetragonal KDP crystals at room temperature. The lattice parameters of this orthorhombic phase are almost the same as in the case of the low temperature ferroelectric phase, a-and b-axes are the diagonals in the tetragonal XY-plane. The most probable space group of the orthorhombic phase is Aba 2. Partially coherent precipitates of about 500-1200 Å in diameter and noncoherent particles of about 1300-4500 Å in size are observed. The concentration of semicoherent particles is about 10¹¹cm⁻³ and volume fractions of noncoherent particles are in the range from 1,0-1,5% to 4,5-5,0% in different crystals. One can distinguish the preferential [110]_t (or [110]_t) direction in the KDP crystals along which the particles are distributed.

Key Words:

• KDP
• TEM
• precipitates of orthorhombic phase