Reply to the comment on 'Orthorhombic to tetragonal structural phase transition in Na_(0.5)K_(0.5)NbO_3-based ceramics' by Laijun Liu et al. Materials Letters (2012)

摘要

We are grateful for the opportunity to reply to the comments on the relationship between monodinic and orthorhombic symmetry. The structure illustration for room temperature is shown in Fig. 1. Although the structure of is orthorhombic at room temperature, as shown in Fig. 1(a). The perovskite type ABO_3 subcell, that possesses mono-clinic symmetry with lattice parameters a_m=c_m＞ b_m while the b_m axis is perpendicular to the a_mc_m plane and angle β a little more than 90° [1-3]. Projection view of the subcell along the b_m axis is shown in Fig. 1(b). Since angle β is very close to 90°, it looks like that a_m axis is also perpendicular to the c_m axis. Therefore, in order to show up the geometrical relationship more clearly, we could exaggerate angle β much more than 90° and draw the projection of monoclinic perovskite ABO_3 subcell, as shown in Fig. 1(c). Furthermore, the relationship between monoclinic and orthorhombic symmetry is shown in Fig. 2. Hence it could be easily understood that the perovskite type subcell of K_(0.5)Na_(0.5)NbO_3 is monoclinic while its unit cell has orthorhombic symmetry at room temperature. That is why the crystal can be described in the monoclinic symmetry instead of orthorhombic one in our paper. Meanwhile, lattice parameters of monoclinic symmetry are convenient to compare with tetragonal symmetry and cubic symmetry.