Fig. 3: Barocaloric effects in 2-D metal–halide perovskites.
From: Colossal barocaloric effects with ultralow hysteresis in two-dimensional metal–halide perovskites
DSC measurements under applied hydrostatic pressure for single-crystal samples of (a) (DA)2MnCl4 and (d) (NA)2CuBr4 with heating and cooling rates of 2 K min−1. Isothermal entropy changes, ΔSit, are calculated by the quasi-direct method for (b) (DA)2MnCl4 and (e) (NA)2CuBr4 for compression from ambient pressure and for decompression to ambient pressure. The shaded area indicates the reversible ΔSit within this pressure range. Isobaric entropy curves are shown in Supplementary Figs. 10 and 11. Direct evaluation of pressure hysteresis, ΔPhys, through quasi-isothermal DSC experiments for (c) (DA)2MnCl4 and (f) (NA)2CuBr4 at 311 K and 306 K, with pressure cycling from 1 to 150 bar and to 105 bar, respectively. ΔPhys is calculated as the difference between the onset pressure for the compression-induced exotherm and the decompression-induced endotherm and is indicated by the horizontal green bar. Variable-temperature powder X-ray diffraction (PXRD) patterns for (g) (DA)2MnCl4 and (i) (NA)2CuBr4 at 360 bar and 300 bar of He, respectively, while cooling from 325 K to 280 K, with an X-ray wavelength of 0.45237 Å. The pressure dependence of the order–disorder transition temperature as determined by HP-DSC (diamonds) and PXRD (squares) is used to calculate the barocaloric coefficient, dT/dP, for (h) (DA)2MnCl4 and (j) (NA)2CuBr4. Red and blue symbols indicate the phase transition temperatures during heating and cooling, respectively. Barocaloric coefficients are summarized in Supplementary Table 8.
