Ferroelectricity in H-bonded H2CsPO4 (CDP) studied by ab initio calculations

J. LASAVE; P. ABUFAGER; S. KOVAL

Porto

Congreso; 13th European Meeting on Ferroelectricity - EMF13 (2015), Porto, Portugal; 2015

Cesium dihydrogen phosphate (CsH2PO4 (or CDP)) is a solid acidcompound that belongs to a large family of H-bonded ferroelectrics whose prominent member isKH2PO4 (KDP). It displays a quasi 1D FE phase transition at atmospheric pressure which differsfrom the 3D nature of the FE ordering observed in KDP. The paraelectric-ferroelectric (PE-FE)phase transition in CDP arises at a critical temperature Tc = 150K. There is a huge isotope effectin the PE-FE transition of CDP with a Tc increase of 110K for the deuterated compound CsH2PO4(DCDP).The microscopic mechanism of the FE transition remains unclear. Also intriguing is the fact thatthe spontaneous polarization Ps is comparable to that of KDP, despite of the different number ofprotons involved in the transition.By Ab Initio methods which are first validated extensively, we study these features as well asperform structural relaxations for CDP. The results are compared to experimental data. We alsoinvestigate the energetics of cluster distortions in the PE phases of CDP and DCDP which arerelevant for their FE transitions and the possibility of cluster tunneling.