The precision determination of the lattice parameters and the coefficients of thermal expansion of BiFeO 3

The lattice parameters of BiFeO 3 were determined with the Straumanis method. At 25–13±0.02 °C, the hexagonal parameters are a h = 5.5799±0.0003, and ch = 13.8670±0.0005 Å. The temperature dependence of the lattice parameters in the range 20–325 °C is given by the equations: a h = 5.5764 Å + 6.06 × 10 −5 t , and c h = 13.8620 Å + 2.10 × 10 −4 t . In the range of 344–838 °C, the lattice parameters obey the following equations: a h = 5.5946 + 6.83 × 10 −5   t , and c h = 13.7251 + 9.05 × 10 −4   t −12.503 × 10 −7   t 2 + 9.40 × 10 −10   t 3 − 3.57 × 10 −13 t 4 . By extrapolation of the angular separation of the 11.0 and the 10.4 reflections, the electrical Curie temperature was determined to be 845±5 °C.