The enlarged XRD patterns in the ra

The enlarged XRD patterns in the range of 2 from 45° to 45.8° are shown in Fig. 6(c). The XRD peaks seem to shift slightly forward to large angle with the increasing temperature, indicating a decrease of lattice parameters of KNN crystals. Since no dopants were added in this study, the reduction of lattice parameters may result from the volatilization of A-site elements such as K and Na. It can be suggested from Fig. 6(c) that the evaporation of alkali ions was much heavier for CS samples, whose XRD peaks exhibited a more distinct shift. Meanwhile, the decrease of cell parameters may also be ascribed to the different molar ratio of sodium and potassium ions since the atom radius of K is larger than Na.[34]