The present disclosure provides nanoparticles of barium zirconium oxide (BaZrO3.BaCO3) and a process for preparation thereof. The present disclosure further provides a coating formulation that chiefly comprises the BaZrO3.BaCO3 nanoparticles along with its method of preparation. Still further, the present disclosure provides X-ray retardant articles and an X-ray retardant preparation for topical application.