ABSTRACT
The structure of room-temperature ZrP2O7 is shown to be orthorhombic by a combination of high-resolution synchrotron powder diffraction and single-crystal synchrotron diffraction data. Small nontwinned single crystals were obtained by synthesizing the compound using solvothermal methods at temperatures below the cubic to orthorhombic phase transition. The average P-O-P angle is 146 degrees. DFT calculations (B3LYP/AUG-cc-pVDZ) on the isolated P2O7(4-) anion yield a P-O-P angle of 153.42 degrees and indicate that the barrier to inversion is of the order 3.6 kJ mol(-1).
ABSTRACT
The thermal transformations of gamma-titanium phosphate, gamma-Ti(PO(4))(H(2)PO(4)).2H(2)O, have been studied using thermogravimetric analysis, differential scanning calorimetry, X-ray powder diffraction, and temperature-resolved in-situ powder diffraction. The transformation sequence goes from gamma-Ti(PO(4))(H(2)PO(4)).2H(2)O over a new partially dehydrated form gamma'-Ti(PO(4))(H(2)PO(4)).(2-x)H(2)O (x approximately 1) to the anhydrous form beta-Ti(PO(4))(H(2)PO(4)) and then through a two-step condensation process where layered titanium pyrophosphate, Ti(PO(4))(H(2)P(2)O(7))(0.5), is formed first and finally cubic titanium pyrophosphate TiP(2)O(7). The dehydration of gamma-Ti(PO(4))(H(2)PO(4)).2H(2)O and the dehydroxylation/condensation process from beta-Ti(PO(4))(H(2)PO(4)) to layered titanium pyrophosphate,Ti(PO(4))(H(2)P(2)O(7))(0.5), was followed in-situ. A new partially dehydrated phase, gamma'-Ti(PO(4))(H(2)PO(4)).(2-x)H(2)O (x approximately 1), which forms at approximately 50 degrees C has been detected and characterized. The unit cell is monoclinic with the lattice parameters a = 23.670(1) Å, b = 6.264(1) Å, c = 5.036(1) Å, beta = 102.41(1) degrees, and Z = 4. Layered titanium pyrophosphate, Ti(PO(4))(H(2)P(2)O(7))(0.5), which forms at 375 degrees C has been characterized. The unit cell is monoclinic with lattice parameters a = 16.271(3) Å, b = 6.319(1) Å, c = 5.122(1) Å, beta = 90.59(2) degrees, and Z = 4.
