Role of correlated disorder on structural stability and functional properties in (Na, Ba)(Nb, Ti)O₃

In perovskites, correlated disorder arises due to chemical substitution and often stimulates the functional properties of these materials. Powder neutron diffraction measurements have been used in conjunction with electrical measurements to investigate the effect of correlated disorder in (1-x)NaNbO3-(x)BaTiO3(NNBTx) solid solution by partially substituting the Ba site with Ca. The effect of correlated disorder on competition and cooperation between polar and antiferrodistortive mode has been investigated. Enhanced dielectric constant (by three times) is observed compared to NNBTx. Emergence/vanishing of diffraction peaks along with change in the intensities is observed in powder neutron diffraction data of (1-x)NaNbO3-x(Ba0.7Ca0.3)TiO3 (NNBCTx). Analysis of this data suggests a structural phase transition with composition change (x), while the phase stability of functional ferroelectric phase at room temperature is extended to lower temperatures. It has also been found that there is a gradual weakening of antiferrodistortive mode (R-4(+)) and presence of spontaneous lattice strain with increasing x. The structural parameters of low-temperature orthorhombic phase of NNBCT05 are modeled in the framework of Gruneisen approximation with a Debye model for the internal energy. (C) 2021 Elsevier B.V. All rights reserved.