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Over the past 60 years, the safe disposal of high-level wastes (HLWs) produced during reprocessing of spent nuclear fuel has become a serious issue and a world-wide challenge. The radionuclides contained in HLWs severely affect the biosphere due to their long half-life and high radiotoxicity. In order to meet this challenging task, the research is underway to develop an advanced stable nuclear waste form which will be capable to accommodate the radiation effects under repository conditions and over geological time scales. Among potential waste forms, zirconolite has been proven to be a good candidate for the desired purpose due to its high radiation and thermal stability and high loading capacity to accommodate the wastes of lanthanides and actinides without any effect on the crystallinity of zirconolite material. In this article, a detailed review has been carried out on ongoing developments in these materials to contain HLWs, various synthesis methods employed to practice these materials, preparation manners of single phase zirconolite compositions and subsequently the structural characterization of zirconolites doped with various tri- and/ or tetravalent lanthanides and actinides as also their loading capacities.

Magnetoelectric (ME) multiferroics are materials in which electric and magnetic dipoles are coupled. The possibility to control electrical properties in the material using magnetic field (and vice versa) in case of ME multiferroics make these materials highly versatile and useful. Over the years many magnetically induced ferroelectrics have been discovered but they show ME effect at low temperature and require high external magnetic field. Recently many Y-type hexaferrites (BaxSr(2-x)Me2Fe12O22), where Me is a divalent cation, have shown ME effect at room temperature and low applied magnetic field, that too in a single phase. Studies suggest that there are several factors that influence the ME properties of Y-type hexaferrites, such as annealing process, the sintering temperature, and ion substitution. It was reported that the lower critical magnetic field was required for inducing electrical polarization when Mg replaces Zn to form Ba2Mg2Fe12O22. Also, it was reported that Strontium doping at Barium site changes the magnetic transition temperature and enhances the ME effects. And it was found that increasing Co content favours high electrical resistivity. Further research and development require careful analysis and compilation of the work on hexaferrites. Y-Type hexaferrite is the focus of this review. Its structure, reason behind ME effect and salient research works has been discussed.