Anisotropic thermal transport properties of quartz: from −120 °C through the α– β phase transition

Thermal diffusivities of synthetic quartz single crystals have been measured between inline-formula−120 and 800 inline-formula^∘C using a laser flash method. At inline-formula−120 inline-formula^∘C, the lattice thermal diffusivities are inline-formulaD_[001]=15.7(8) mminline-formula² sinline-formula⁻¹ and inline-formulaD_[100]=8.0(4) mminline-formula² sinline-formula⁻¹ in the [001] and [100] directions, respectively. Between inline-formula−80 and 560 inline-formula^∘C, the temperature dependence is well approximated by a inline-formula $M17inlinescrollmathmlD\left(T\right)=\mathrm{normal\; 1}/T^n$ 61pt14ptsvg-formulamathimgdc11742a225035490c9431280d82ac6e ejm-33-23-2021-ie00001.svg61pt14ptejm-33-23-2021-ie00001.png dependency (with inline-formulan=1.824(29) and inline-formulan=1.590(21) for the [001] and [100] directions), whereas for lower temperatures measured thermal diffusivities show smaller values. The anisotropy of the thermal diffusivity inline-formulaD_[001]∕D_[100] decreases linearly over inline-formulaT in inline-formulaα- and inline-formulaβ-quartz, with a discontinuity at the inline-formulaα–inline-formulaβ phase transition at inline-formula $M26inlinescrollmathml{T}_{\mathrm{italic\; \alpha },\mathrm{italic\; \beta }}=\mathrm{normal\; 573}$ 53pt14ptsvg-formulamathimgc326afa62d4b1b7b0014c117925b6e7f ejm-33-23-2021-ie00002.svg53pt14ptejm-33-23-2021-ie00002.png  inline-formula^∘C. In the measured signal–time curves of inline-formulaα-quartz, an unusual radiative heat transfer is observed, which can be linked to the phase transition. However, the effect is already observed far below the actual transition temperature. The standard evaluation procedure insufficiently describes the behaviour and leads to an underestimation of the thermal diffusivity of inline-formula≥20 %. Applying a new semi-empirical model of radiation absorption and re-emission reproduces well the observed radiative heat transfer originating in the phase transition. In the inline-formulaβ-quartz region, the radiative heat transfer is not influenced by the phase transition effect observed in inline-formulaα-quartz and for the thermal diffusivity evaluation common models for (semi)transparent samples can be used.