The precision determination of the lattice parameters and the coefficients of thermal expansion of BiFeO₃

The lattice parameters of BiFeO₃ 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^-5t, and c_h = 13.8620 Å + 2.10 × 10^-4t. 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 t² + 9.40 × 10^-10 t³ - 3.57 × 10^-13 t⁴. 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.