We report the compressibility of two Prussian blue analogs (PBAs) under hydrostatic pressure, one with small and one with a relatively large cubic unit cell among PBAs, and investigate the modification of their elastic properties when the two lattices are coupled within a heteroepitaxial core–shell structure. Bulk modulus (K₀) values are derived from x-ray powder diffraction experiments using a diamond anvil cell with silicone oil as a pressure-transmitting medium. The pressure–volume curves fitted to Murnaghan equations of states show that K₀ inversely scales with the crystal packing for the rubidium cobalt hexacyanoferrate and rubidium nickel hexacyanochromate samples (K₀ ∼ 29 GPa for Co-Fe PBA, a₀ = 9.95 Å and ∼20 GPa for Ni-Cr PBA, a₀ = 10.48 Å with a₀ being the lattice constant at ambient pressure). The two single-phase samples undergo a cubic-to-rhombohedral phase transition above ∼0.8 GPa, which correlates fairly well with the build-up of nonhydrostatic pressure contributions in the cell. Within the core–shell structure, the volume change observed for the core scales with that of the shell because of the configuration close to the case of a solid pressure-transmitting medium. The Ni-Cr PBA shell layer exhibits an increased rhombohedral distortion with respect to the single-phase reference possibly associated with shearing at the core–shell interface. Its bulk modulus is not significantly modified with respect to that of the single-phase sample despite the presence of defects associated with the growth mode, whereas the P-V curve of the core suggests a stiffening of the Co-Fe PBA lattice.

中文翻译：

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由普鲁士蓝类似物制成的异质外延核壳颗粒的高压行为

我们报告了两种普鲁士蓝类似物 (PBA) 在静水压力下的可压缩性，一种在 PBA 中具有较小的立方晶胞，另一种具有相对较大的立方晶胞，并研究了当两个晶格在异质外延核内耦合时它们的弹性特性的改变——壳结构。体积模量 ( K ₀ ) 值来自 X 射线粉末衍射实验，使用金刚石砧座，硅油作为压力传输介质。拟合 Murnaghan 状态方程的压力-体积曲线表明，K ₀与六氰基铁酸钴铷和六氰铬酸铷镍样品的晶体堆积成反比（ Co-Fe PBA 的K ₀ ∼ 29 GPa，a₀  = 9.95埃和〜20 GPA为镍铬PBA，一个₀  = 10.48带有一个₀是环境压力下的晶格常数）。两个单相样品在约 0.8 GPa 以上经历了立方到菱形的相变，这与电池中非静水压力贡献的积累非常相关。在核壳结构中，由于结构接近于固体压力传输介质的情况，观察到的核的体积变化与壳的体积变化成比例。Ni-Cr PBA 壳层相对于单相参考表现出增加的菱形畸变，这可能与核壳界面处的剪切有关。尽管存在与生长模式相关的缺陷，但相对于单相样品，其体积模量没有显着改变，而P - V 核心的曲线表明 Co-Fe PBA 晶格变硬。