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 ah = 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: ah = 5.5764 Å + 6.06 × 10−5t, and ch = 13.8620 Å + 2.10 × 10−4t. In the range of 344–838 °C, the lattice parameters obey the following equations: ah = 5.5946 + 6.83 × 10−5 t, and ch = 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.