Once More About the "Forbidden" Domain Structure and the Isolated Point in K2Cd2xMn2(1-x)(SO4)3 Langbeinites

TL;DR

This study investigates the domain structures and phase transitions in K2Cd2xMn2(1-x)(SO4)3 langbeinites, revealing enantiomorphous domain walls, phase symmetry changes, and identifying an isolated point at x=0.6 in the phase diagram.

Contribution

It provides new insights into the domain wall structures, phase symmetry transformations, and the phase diagram of langbeinites with varying composition.

Findings

Domain walls separate enantiomorphous states in ferro-elastic langbeinites.

Phase symmetry changes from 23 to 222 involve domain wall transformations.

An isolated point at x=0.6 in the phase diagram was identified.

Abstract

The domain structure in K2Cd2xMn2(1-x)(SO4)3 (x=0.5, 0.7 and 0.9) langbeinite crystals is studied with the aid of optical polarization microscopy. It is shown that the domain walls in ferro-elastic langbeinites separate enantiomorphous orientation states. These orientation states appear in the phase with the symmetry 23 in connection with the hypothetic phase transition . In the phase with the symmetry 222, these domain walls are transformed to those separating ferroelastic domains with the opposite signs of enantiomorphism. It is revealed that one enantiomorphous domain can only transform to the other via a thick layer of the parent phase with symmetry. The results for the volume thermal expansion are presented. It is shown that the isolated point at the x,T-phase diagram of K2Cd2xMn2(1-x)(SO4)3 solid solutions corresponds to the concentration x=0.6.