Spontaneous strain of mixed crystal system [N(CH3)4]2ZnBr4-[P(CH3)4]2ZnBr4

Spontaneous strain accompanied by the ferroelastic phase transition of the mixed crystal system [N1-xPx(CH3)(4)](2)ZnBr4 (x = 0, 0.05, 0.15, 0.44, 0.75, 0.85, 0.93: 1) was studied by X-ray diffraction. The deviation angle Delta beta of the monoclinic angle beta from 90 degrees showed characteristic temperature dependence: where the sign of Delta beta was chosen so that the configuration of ions in the ferroelastic phase was the same for all compositions. As the value of x increased to 0.15, the maximum value of Delta beta increased and the slope in the low-temperature region decreased. At x = 0.44, Delta beta was almost temperature independent. Absolute values were very small at a:= 0.75. At x = 0.85 it was negative throughout, and above the concentration it approximated the typical temperature dependence of [P(CH3)(4)](2) ZnBr4. The transition temperature increased with increasing a;. The phase transition changed from second order to first order one between x= 0.85 and 0.93. Structure analysis revealed that the position of ions changed only slightly in the ferroelastic phase in each compound.