Complex structural evolution in BaTiO3 single crystals caused by the coexistence of competing anharmonic potentials

BaTiO3 (BTO) was the first ferroelectric perovskite oxide discovered in the 1940′th.. It was also the first ferroelectric compound without hydrogen bonds. Its wide applicability, together with its simple cubic structure, directly intensified and inspired research on perovskite oxides, leading to the discovery of many additional oxides. Although known for more than 80 years, refined and newly developed high-resolution experimental techniques have uncovered novel results that have advanced physical insight into this material, which are challenging for theoreticians, and there is a need for novel ideas. Here we show that the complex phase diagram of BTO can be understood based on the coexistence of a double-well potential and a sixth-order one, where the former is related to the polarizable cluster mass TiO6, and the latter describes the local dynamics of the Ti ion in the octahedral cluster. In light of new results from birefringence experiments, the phase diagram of BTO is reinterpreted.