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The emerging phase change materials (PCMs) have attracted much attention due to their unique properties and applications. However, the optical properties of PCM at high pressures have not been well explored. In this work, the microstructure and optical properties of GeTe and Sn-substituted GeTe at high pressures up to 30 GPa have been systematically investigated. We find that the substitution of small amounts of Sn for Ge combined with the introduction of high pressure can induce an optical contrast of 117% in crystalline GeTe, which is even higher than the highest optical contrast reported so far (90%) caused by amorphous GeTe to crystalline GeTe. The pressure-induced contrast does not originate from any phase transition as previously, but from the combined effect of Peierls distortion elimination and Ge vacancy formation, which leads to an increase in carrier concentration. The relationship between pressure/atomic composition, Peierls distortion/vacancy formation, and optical contrast can be well explained by a combination of experiments and theoretical calculations. Therefore, this study reveals the effect of high pressure on the optical properties of PCMs and provides new ideas for the design of high-optical-contrast PCMs. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) are recognized as a promising passive energy retrofit technology for existing buildings, as they are applied to the internal and external surfaces of the building with less impact on the original structure. However, the effectiveness of PCMs varies from region to region. Taking the Central Plains of China as an example, this paper investigated the effect of phase change temperature and material thickness variation on the energy efficiency of PCM when it was arranged on 14 placements including furniture through EnergyPlus (E+). And further explored the applicability of coupling PCMs with natural ventilation (NV). The results showed that: for the Central Plains of China, PCMs arranged on the internal surface of building roofs were optimal, and the reduction rate of uncomfortable degree hours could reach 38%, 26%, 24% and 40% after integrating PCMs into the roof, floor, external wall and furniture. The uncomfortable degree hour reduction rate per unit mass of PCM was 0.052%/kg for the roof, and the value of furniture was very close to the external wall and floor, which achieved 0.033%/kg. In addition, the coupling of PCM with NV improved the energy efficiency of PCM by more than twice. [ABSTRACT FROM AUTHOR]