Lithium niobate (LN) and lithium tantalate (LT) are highly attractive ferroelectric materials for electronic devices like filters, oscillators, and sensors. The pursuit of superior electro-optical, piezoelectric, and acoustic properties, combined with low-temperature dependence, makes them a preferred choice.

The investigation of the structural phase transition in the vicinity of the Curie temperature Tc of LiNb_1−xTa_xO₃ crystals is motivated by the expected combination of advantageous high-temperature properties of LiNbO₃ and LiTaO₃, including high piezoelectric modules and remarkable high-temperature stability, respectively.

This study aims to uncover and explain changes in electrical conductivity that accompany the phase transition for various compositions x in LiNb_1−xTa_xO₃. Our investigation involves experimental methods such as measuring electrical conductivity even above T_c, calorimetry, and ab initio molecular dynamics calculations executed on large supercells.

Based on the logarithmic slopes of the conductivity in Figure 2, it has been observed that the latter provides an elegant approach to determine T_c. The conductivity slope also shows a significant change in the activation energy during the transition, which reflects T_c. The observation can be attributed to the unique distribution of Li ions on the octahedral sites. In addition, with increasing temperature and low Ta content x, polaron transport contributes more significantly to changes in conductivity. Furthermore, molecular dynamics calculations indicate that cation displacements occur below the transition temperature for LiNbO₃ and LiTaO₃, as well as for LiNb_1-xTa_xO₃. These displacements can affect the properties of the materials even below T_c. Calorimetry data and the ab initio modelling are in good agreement with T_c deduced from the electrical conductivity.