Determination of thermal expansion of germanium, rhodium and iridium by X-rays

The lattice parameters of germanium, rhodium and iridium were measured with a Unicam 19 cm high-temperature powder camera; the following equations represent the results: Ge: a_t = 5.6569 + 34.22 × 10^-6t + 10.17 × 10^-9t² - 0.66 × 10^-12t³, Rh: a_t = 3.8026 + 29.27 × 10^-6t + 10.49 × 10^-9t² + 0.54 × 10^-12t³, Ir: a_t = 3.8383 + 23.52 × 10^-6t + 4.92 × 10^-9t² + 0.89 × 10^-12t³. Thermal expansion coefficients and Grüneisen parameters were also calculated.