Shakila Nur The first reference appears to be (Wikipedia):

Smolenskii, G.; Isupov, V.; Agranovskaya, A.; Krainik, N. (1961). "New ferroelectrics of complex composition". Sov. Phys. Solid State. 2: 2651–2654

See also: Giuseppe Viola, Ye Tian, Chuying Yu, Yongqiang Tan, Vladimir Koval, Xiaoyong Wei, Kwang-Leong Choy, Haixue Yan,

Electric field-induced transformations in bismuth sodium titanate-based materials, Progress in Materials Science, Volume 122, 2021, 100837,

ISSN 0079-6425,

https://doi.org/10.1016/j.pmatsci.2021.100837.

(https://www.sciencedirect.com/science/article/pii/S007964252100061X)

See also the attached thesis.

Really appreciate and thank you very much for your kindness and answer to me Prof @Alan F Rawle

Dear Shakila Nur please do recommend my answer if helpful.

Sodium Bismuth Titanate, commonly known by its chemical formula Na0.5Bi0.5TiO3 (NBT), is a type of ferroelectric material with potential applications in the field of piezoelectric devices and ferroelectric ceramics. The development and study of NBT have involved the contributions of various researchers over time, and it may not have a single founder or pioneer.

The exploration of NBT and related materials is part of ongoing research in the broader field of ferroelectric ceramics and solid-state physics. Researchers and scientists from different institutions around the world have contributed to the understanding, synthesis, and applications of NBT.

If you are looking for specific information on the early history or notable contributors to the development of NBT, it's recommended to consult scientific literature, research papers, or review articles on ferroelectric ceramics and perovskite materials. Authors who have made significant contributions to the understanding of NBT may be mentioned in relevant research papers or reviews within the field.