Periodic transition of microcrystals on the host (110) face of KLu(WO₄)₂ crystals

The interesting morphology of the (110) face of laser-active potassium lutetium tungstate, KLu(WO₄)₂ (KLuW), crystals has been investigated with an Opton polarizing microscope. Three microcrystals with regular shapes are formed on the edge of the host (110) surface; furthermore, their shapes have a 180° rotation relationship with each other. It is suggested that the three microcrystals may be the representatives of different growth stages, indicating that a periodic transition occurs during the process of crystal growth. In addition, the morphologies of the steps spreading from the three microcrystals and the inner growth sources are very different. The shape of the observed microcrystal is predicted and the formation mechanisms are carefully analyzed. The observed periodic transition morphologies are thought to imply some profound physical background. Unfortunately, until now no universally accepted theory has been able to elucidate the periodic transition phenomena.