Unexpected differences in the properties of orthovanadates(V) of rare earth metals obtained by different synthesis methods

Orthovanadates(V) of rare earth elements with the general formula REVO4 (RE = Y, Yb, Er) were obtained by the following methods: high-temperature solid state reactions and mechanochemical method in a high-energy planetary ball mill. These compounds were also synthesized for the first time by sonochemical method from substrates: RE(NO3)3 (RE = Y, Yb, Er) with NH4VO3. Single-phase samples of REVO4 were examined using XRD, DTA, SEM, FTIR and UV–Vis-DR methods. The results obtained established that the crystallite sizes of REVO4 compounds (RE = Y, Yb, Er) obtained by mechanochemical and sonochemical methods are nanometric ranging from ~ 10 nm to ~ 20 nm. In addition, REVO4 compounds were confirmed to crystallize in a tetragonal system, the parameters of their elemental cells were calculated and shown to be isostructural. It was shown that as the ionic radius of RE3+ decreases, the volume of REVO4 elementary cells decreases. Estimated for REVO4, the width of the excited energy band ranges from ~ 2.66 eV to ~ 3.66 eV, which means that these compounds belong to the class of semiconductors. The lowest energy bandgap value among all the obtained orthovanadates was for YVO4 obtained by high-temperature solid state reactions.