THERMOSTRUCTURAL PROPERTIES OF A NEW VANADATE, Ca9.5Mn(VO4)7: THERMAL EXPANSION AND SEARCH FOR SUBSTITUTIONAL DISORDER OF MANAGNESE

β-calcium orthophosphate and calcium orthovanadate, are known to crystallize in R3c space group. some fraction of Ca atoms can be replaced by other ones,of valences from +1 to +4, without a change of structure. The presence of transition metal (TM) in the TCP lattice may be advantageous from the biomedical application point of view and can be applicable for white LEDs. We are interested in studying of the new whitlockite material,Ca10.5-xTMx(VO4)7.We already determined structural properties at room temperature. The unit cell is quite large with many tens of parameters to be fitted,therefore the laboratory data collected with a HT attachment do not give information about the crystal structure. The aim of proposed study is a careful refinement of the structure. It is expected order-disorder transition for our material and instead of residing solely at M5 site, the TM ions will transfer,with raising T,to one or more from among M1-M4 sites, causing a nonlinearity in thermal expansion runs