The use of solid-solid phase change materials within thermal energy storage has garnered increased attention due to their higher energy densities, lack of requirement for encapsulation and smaller volume fluctuations reported compared to their solid-liquid counterparts. Focus is placed on identifying appropriate tetrahedral complexes within a broad range, and analysing the thermal capabilities and structural integrity across cycling through DSC and PXRD, to further understand the relationship between the solid-solid transition and latent heat storage. The thermal positioning of these transitions is shown for KBF4, NaBF4, Na2MoO4, K2MoO4 and Na2SO4, as well as enthalpic capability. All materials present cycling thermal stability within DSC, but identification of phases remains qualitative for Na2MoO4, K2MoO4 and Na2SO4. The phase transition temperatures from diffraction measurements are consistent with the thermal analysis data for tetrafluoroborates and subsequent Rietveld Refinements are conducted revealing temperature effects on lattice parameters. This proved the pre-existing knowledge of the Pnma to Fm-3m transition within KBF4 with assurance and the crystal structure of high-temperature NaBF4 phase has been determined. The high-temperature disordered phase of NaBF4 crystallizes in the hexagonal, space group P63/mmc with a = 4.98955(1)Å, c = 7.73498(3)Å, V = 166.768(1) Å3, and Z = 2 at 250 °C. Thermal conductivity measurements of both KBF4 and NaBF4 were obtained in the temperature range 25 – 300 °C using a laser flash apparatus, showing a gradual decrease up to the transition temperature and then rose slightly.
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