Structural parameters determining the transition temperature of tetragonal KH2PO4-type crystals

A systematic study of the structural parameters determining the ferroelectric phase transition temperature Tc in tetragonal KH2PO4 (KDP)-type crystals MH2XO4 has been performed by searching the correlation between different structural parameters and Tc. It has been revealed that the transition temperature is determined not only by the hydrogen-bond distance R, as reported earlier, but also by the distortion of XO4 (via O-X-O angle α1) and the packing of M and XO4 along the c axis (via the rotation angle θ around the c axis); α1 reflects the dipole moment of XO4 and θ may influence the amplitude of optical vibration of M and XO4. The contribution of each structural part to the transition temperature Tc in the tetragonal KDP family has been revealed in a comprehensive way for ferroelectrics.