Effect of Ti4+ and Pb2+ on negative thermal expansion and polarization behaviors of KSr2Nb5O15: First-principles investigation

Abstract

The utilization of both negative and positive thermal expansion coefficients presents a potential means of mitigating internal stress in high-temperature materials, hence offering a novel approach to enhance the impact strength of those materials. The investigation of the thermal expansion coefficient and polarization characteristics of KSr2Nb5O15 doped with Ti4+ and Pb2+ was conducted by the utilization of first-principles calculations. The introduction of Ti4+ and Pb2+ into the KSr2Nb5O15 lattice resulted in an increase in lattice distortion. This effect was particularly pronounced when Ti4+ and Pb2+ were co-doped, leading to the largest lattice distortion observed in KSr2Nb5O15. Furthermore, the negative thermal expansion coefficient of KSr2Nb5O15 was also found to be the highest under these co-doping conditions, with a value of −0.560×10−5 K−1 compared to the original value of −0.011×10−5 K−1. Conversely, when Ti4+ was doped individually, the lattice distortion and negative thermal expansion coefficient of KSr2Nb5O15 were found to be the smallest. Furthermore, the inclusion of Ti4+ and Pb2+ leads to an enhancement in the dielectric constant. This effect is particularly pronounced when Ti4+ and Pb2+ are simultaneously incorporated into the KSr2Nb5O15 lattice. Consequently, the dielectric constant of the material exhibits a substantial improvement. The greatest polarization intensity is achieved when KSr2Nb5O15 is co-doped with Ti4+ and Pb2+, resulting in a polarization intensity of 38.61 μC/cm2. The dense ceramics comprising of KSr2Nb5O15, with the addition of Ti4+ and Pb2+ dopants, were synthesized using the solid-state reaction method. Subsequently, the thermal expansion coefficients and dielectric characteristics of these ceramics were evaluated. The experimental results are not in good agreement with the calculated results, but qualitatively, the trend predicted by the theory is confirmed by experiment. This study establishes the groundwork for the synthesis of KSr2Nb5O15 materials exhibiting pronounced negative thermal expansion characteristics.