Recently, ABO 4 -type ternary metal oxides have received considerable attention because of their wide range of properties and applications in fundamental physics, chemistry, and materials science. [1][2][3] Exploring the ABO 4 materials is both challenging and interesting because of the variety of structures that have been observed in these oxides. The most common structural types are scheelite, zircon, wolframite, monazite, baryte, fergusonite, and pseudoscheelite. These all contain BO 4 tetrahedra and temperature-and/or pressure-induced structural phase transitions between these are well documented; for example, the transformation from monazite to scheelite to zircon with increasing temperature and from zircon to monazite to scheelite with increasing pressure. [4] This structural versatility leads to a variety of physical features that enables a diverse and broad range of applications, distinguishing ABO 4 -type compounds from other materials. Applications include phosphors (ZrGeO 4 and HfGeO 4 ), battery materials (CaMoO 4 and SrWO 4 ), laser host materials (BaWO 4 and GdTaO 4 ), and scintillators (CdWO 4 and PbWO 4 ). [5] High pressure studies show that the scintillating properties of orthovanadates are better when compared to periodates. [6][7][8] Our recent study suggests that thallous perchlorate and perbromate can be used as inorganic scintillators, since there exists a charge-transfer character in the bands. [9] It is generally found that the structure of the ABO 4 oxides favored under ambient conditions is dependent on the smaller, more highly charged, B-type cation. Phosphates, silicates, vanadates, chromates, and arsenates are known to crystallize in the zircon-type structure, although several phosphates and arsenates crystallize in the quartz structure, whereas the scheelite structure is observed for numerous molybdates, tungstates, iodates, and germanates. [10] The ABO 4 -type compounds where B is technetium (Tc), that is, the pertechnetate group (TcO À1 4 ) have been less well explored. Tc is the first man-made transition metal, and it is the lightest radioactive synthetic element. Tc is the mostly widely utilized radiopharmaceutical and it has been found useful as a corrosion inhibitor in the steel industry, as a superconductor at a very low temperature [11] and also as an environmental water tracer. [12,13] Transition-metal oxides are fascinating to study because of their high melting temperatures and densities, and the capacity of transition metals to form compounds with other elements as well as the potential for transmutation from one compound to another. [14,15] Of the 21 known isotopes of Tc, 99 Tc is the most abundant, and it is a significant by-product of the fission of
