High-pressure structural investigation on lead-free piezoelectric 0.5Ba(Ti 0.8 Zr 0.2)O 3-0.5(Ba 0.7 Ca 0.3)TiO

An experimental platform for dynamic diamond anvil cell (dDAC) research has been developed at the High Energy Density (HED) Instrument at the European X-ray Free Electron Laser (European XFEL). Advantage was taken of the high repetition rate of the European XFEL (up to 4.5 MHz) to collect pulse-resolved MHz X-ray diffraction data from samples as they are dynamically compressed at intermediate strain rates (≤103 s−1), where up to 352 diffraction images can be collected from a single pulse train. The set-up employs piezo-driven dDACs capable of compressing samples in ≥340 µs, compatible with the maximum length of the pulse train (550 µs). Results from rapid compression experiments on a wide range of sample systems with different X-ray scattering powers are presented. A maximum compression rate of 87 TPa s−1 was observed during the fast compression of Au, while a strain rate of ∼1100 s−1 was achieved during the rapid compression of N2 at 23 TPa s−1.

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Understanding the high-pressure behavior of ammonia hydrates is relevant for modeling the interior of solar and extrasolar icy bodies. We present here the results of high-pressure x-ray diffraction studies on ammoniadihydrate (ADH) at room temperature (298 K) up to 112 GPa, employing both static and dynamic compression experiments performed in diamond anvil cells. The derived pressure-volume (P-V) compression curves are in excellent agreement regardless of the compression technique. In contrast to early theoretical predictions, our results indicate the stability of the disordered molecular alloy (DMA) phase, a body centered cubic (bcc) structure, and the absence of self-ionization in the investigated pressure range. By combining the P-V data from seven different compression runs, we derive the first equation of state for ADH-DMA based on the third-order Birch-Murnaghan formalism with best-fit parameters: V 0 = 23.96 ± 0.03 (Å 3 /molecule), B 0 = 9.95 ± 0.14 GPa, and B 0 = 6.59 ± 0.03. The instantaneous bulk modulus directly derived from the quasicontinuous compression curves displays a smooth increase upon compression that further supports the absence of structural transitions.