Abstract
The structure of NaTi 2(PO 4) 3 shows the space group R3̄c, whereas that of NaSn 2(PO 4) 3 presents the space group R3̄ at room temperature and it undergoes a second order phase transition at 575°C from this structure to another with the space group R3̄c. Evolution of the structure of NaTi 2(PO 4) 3NaSn 2(PO 4) 3 solid solutions with temperature has been studied and temperature phase transition established for the compositions studied. Lattice thermal expansion of NaTi 2−xSn x(PO 4) 3 solid solutions with x = 1, 1.2, 1.5 has been determined from x-ray diffraction data at temperatures ranging from 26 to 1000°C. DSC and dilatometric measurements have been also carried out on these samples. The composition with x = 1.5, NaTi 0.5Sn 1.5(PO 4) 3, presents a second order phase transition at 355°C, from the phase with R3̄ space group to the phase with R3̄c space group, similar to that of the compound with x = 2, NaSn 2(PO 4) 3. For the solid solution with x = 1.2, NaTi 0.8Sn 1.2(PO 4) 3, this transition seems to occur at a temperature closed to the room temperature, whereas the composition with x = 1, NaTiSn(PO 4) 3, does not show any phase transition. Thermal expansion of these solid solutions for x < 1.2 is more similar to that of NaTi 2(PO 4) 3 whereas for x > 1.2 is analogous to that of NaSn 2(PO 4) 3.
Published Version
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