Effect of seeds and sintering additives on (K,Na,Li)NbO₃ leadfree single crystals grown by a solid-state crystal growth method

A solid-state crystal growth (SSCG) method has been utilized to prepare (K_0.45Na_0.55)_0.94Li_0.06NbO₃ (KNLN) lead-free piezoelectric single crystals. The effects of different kinds of seeds and additives on K_0.5Na_0.5NbO₃ (KNN)-based crystal growth were studied. It was found that (100)-oriented SrTiO3 seed was inappropriate for growing KNLN single crystal, while (100)- oriented KTaO3 one could act as a good seed. The inverse pole figure (IPF) showed that the epitaxial layer was indeed single crystal and oriented in the same (100) direction as the seed. Addition of 0.5 mol% ZnO, CuO and MnO2 brought liquid phase in the samples and increased the diffusion rate of the atoms. This would finally enhance both the single crystal and the matrix grain growth. Among all the sintering additives, CuO could increase the matrix grain growth remarkably due to the assistance of the largest amount of the Na-deficient liquid phase, whose composition was time-independent. However, CuO was not the most effective one that can promote the single crystal growth. The reasons might be as follows: (1) the liquid accumulation at the interface of the single crystal/matrix lead to the liquid phase content exceeding the critical value in the CuO-added samples, which increased the diffusion distance and partly offset the enhanced diffusion rate; (2) the large matrix grains brought low driving force for crystal growth.