Detection of twinning in KNaSO4 crystals by electron paramagnetic resonance and by x-ray diffraction

The Laue symmetry and twinning in KNaSO4 crystals grown from the melt were studied by electron paramagnetic resonance (EPR) and by x-ray diffraction. The rotation patterns and signal intensities of the SO4- free radical produced by -ray irradiation were studied by the EPR method, and the diffraction patterns and intensities of the Laue method and the precession method were studied by x-ray diffraction. The EPR results indicate that the Laue symmetry is of the same class as the trigonal D3 symmetry, and that the possible twin operations include a twofold rotation about the c axis, a sixfold rotation about the c axis, the 112» twofold rotations, and the {112»0} mirror reflections. The x-ray results indicate that the true Laue symmetry is the trigonal 3»m, and that twinning is of the merohedral type, which is consistent with the finding by the EPR method. Both the EPR and the x-ray method indicate that the fraction of twinning is less than 1 in pure KNaSO4 crystals, but approaches 1 in Cd2+-doped crystals. The x-ray diffraction patterns and intensities of Cd2+-doped crystals approach those expected for ideal hexagonal crystals, which suggests that twinning in KNaSO4 crystals is in the form of twin domains.