The present disclosure provides nanoparticles of barium zirconium oxide (BaZr03.BaC03) and a process for preparation thereof. The present disclosure further provides a coating formulation that chiefly comprises the BaZr03.BaC03 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.