Synchrotron x-ray diffraction studies of the $\alpha \rightleftharpoons \beta$ structural phase transition in Sn and Sn-Cu

The transformation between the metallic ($\beta$) and semi-conducting ($\alpha$) allotropes of tin is still not well understood. The phase transition temperature stated in the literature, 286.2 K, seems to be inconsistent with recent calorimetric measurements. In this paper, this intriguing aspect has been explored in Sn and Sn-Cu (alloyed 0.5% Cu by weight) using temperature resolved synchrotron x-ray diffraction measurements performed at the Indus-2 facility. Additionally, the $\alpha \rightleftharpoons \beta$ Sn transition has been recorded using in-situ heating/cooling experiments in a scanning electron microscope. Based on these measurements, a protocol has been suggested to reduce the formation of $\alpha$-Sn in potentially susceptible systems. This will be useful in experiments like TIN.TIN (The INdia-based TIN detector), which proposes to employ ~100 - 1000 kg of superconducting tin-based detectors to search for neutrinoless double beta decay in the isotope $^{124}$Sn.