X-ray study of ferroelastic phase transition in CsLiCrO₄ crystals

Abstract

Cesium Lithium Chromate CsLiCrO₄ crystals are crystallized from aqueous solution in two types with pseudohexagonal and cubic structures. Pseudohexagonal crystal undergoes a second-order phase transition at T_c = 427 K from orthorhombic Pmcn to monoclinic P112₁/n. The deviation Δ_γH(T) = _γH(T) −90° of monoclinic angle _γH(T) from 90° has been measured by X-ray diffraction in the temperature range from 460 K down to 10 K. It is found that Δ_γH(T) increases continuously from zero at the transition temperature T_C = 427 K, and reaches maximum value at T _max = 355 K, and changes its sign at the compensation temperature T_Z = 130 K, and tends to saturate around 15 K. Cubic crystal belongs to cubic F 43m at room temperature. Lattice constant a_C (T) has been measured by Bond method in the temperature range from 299 K down to 10 K. It is found that cubic crystal undergoes a first-order phase transition at T_C1 = 89 K, and also shows anomaly around T_A = 63 K in X-ray intensity profiles.

Key Words:

• CsLiCrO₄
• pseudohexagonal structure
• cubic structure
• monoclinic angle
• ferrielastic
• phase transition