Thermal expansion of manganese dioxide using high-temperature in situ X-ray diffraction

High-temperature in situ X-ray diffraction is used to determine the thermal expansion behaviour of manganese dioxide in air at temperatures between 298 and 673 K, the range accessible prior to material decomposition. Two manganese dioxide samples of different origins are investigated to observe the effect of synthesis conditions and resultant material properties on the thermal response. β-MnO₂ prepared by a chemical pathway is found to expand linearly over the temperature window with thermal expansion coefficients (in units of K⁻¹) of α_a = 9.3 (4) × 10⁻⁶, α_c = 7.0 (2) × 10⁻⁶ and β = 25.6 (8) × 10⁻⁶. Conversely, the thermal expansion of heat-treated electrolytic manganese dioxide is disjointed about 473 K in the a direction and for the overall unit-cell volume, and about 523 K in the c direction. Coefficients are therefore given (in units of K⁻¹) as α_a = 23 (4) × 10⁻⁶ (298–473 K), 10 (3) × 10⁻⁶ (473–673 K); α_c = 0.2 (9) × 10⁻⁶ (298–523 K), 10 (1) × 10⁻⁶ (523–673 K); and β = 49 (9) × 10⁻⁶ (298–473 K), 26 (5) × 10⁻⁶ (473–673 K).