Lattice thermal expansion of sodium metaperiodate, NaIO₄

The lattice parameters and the principal coefficients of thermal expansion of sodium metaperiodate have been determined at different temperatures. The temperature dependence of the two coefficients, α_a along the a axis and α_c along the c axis, could be expressed in the following forms: α_a = 36.57 × 10⁻⁶ + 4.89 × 10⁻⁸ t + 14.19 × 10⁻¹¹ t² // α_c = 49.43 × 10⁻⁶ + 18.42 × 10⁻⁸ t − 9.22 × 10⁻¹¹ t². Here t is the temperature (°C). The results have been compared with authors' earlier data on potassium metaperiodate. It is pointed out that the difference in the behaviour of the two isotypic crystals is due to the small but significant structural changes produced by the different sizes of the two metal ions.