Structure and Phase Transitions of SnP2O7 |
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Authors: | R.K.B GoverN.D. Withers S. AllenR.L. Withers J.S.O. Evans |
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Affiliation: | a Department of Chemistry, University of Durham, South Road, Durham, DH1 3LE, United Kingdomb Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia |
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Abstract: | SnP2O7 is a member of the ZrP2O7 family of materials, several of which show unusual thermal expansion behavior over certain temperature ranges and which show a number of displacive phase transitions on cooling from high temperature. Here we describe the structural properties of SnP2O7 from 100 to 1243 K as determined by X-ray and neutron powder diffraction. These studies reveal that SnP2O7 shows two phase transitions in this temperature range. At room temperature the material has a pseudo-cubic 3×3×3× superstructure. Electron diffraction studies show that the symmetry of this structure is P213 or lower. On warming to ∼560 K it undergoes a phase transition to a structure in which the subcell reflections show a triclinic distortion; above 830 K the subcell reflections show a rhombohedral distortion. Significant hysteresis in cell parameters is observed between heating and cooling. The structure of SnP2O7 is discussed with references to other members of the AM2O7 family of materials. |
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Keywords: | tin pyrophosphate thermal expansion X-ray diffraction electron diffraction neutron diffraction phase transitions. |
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