Synthesis, symmetry, and physical properties of cerium pyrophosphate

CeP2O7, a close structural relative of ZrP2O7, and many other (MX2O7)-X-IV (X - P, V, As) phases, forms on heating Ce(HPO4)(2)center dot xH(2)O between similar to 300 and 600 degrees C and decomposes by oxygen loss at higher temperatures. In-situ X-ray diffraction measurements showed, for some precursor batches, the formation of CeP2O7 in two distinct stages. At room temperature,. CeP2O7 is pseudocubic, but probably triclinic, displaying positive thermal expansion below similar to 115 degrees C. Above this temperature, there is a transition to cubic symmetry (Pa (3) over bar) with the linear coefficient of thermal expansion going to zero at similar to 450 degrees C and becoming negative at higher temperatures. CeP2O7 probably undergoes two phase transitions on compression below similar to 10.5 GPa. The phase existing between 0.65 and similar to 5 GPa is soft with an average bulk modulus of similar to 18 GPa.