Crystal Structure of Six-Layer Ba1-xSrxRuO3

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We have synthesized the polycrystalline Ba1-xSrxRuO3 for $0\leq x \leq 1.0$, and investigated the crystal structure by X-ray powder diffraction. The crystalline structure of Ba1-xSrxRuO3 of six-layer phase at around $0.4 \leq x \leq 0.8$ is clarified to be six-layer monoclinic with $C2/c$ symmetry. The high-temperature X-ray diffraction experiment revealed the structural transition between the six-layer monoclinic and six-layer hexagonal structure with $P6_{3}/mmc$ around 580 K for $x=0.5$. For $x=0.6$ and 0.7, the monoclinic distortion decreases with increasing temperature though the transition was not observed below 623 K. The phase diagram of the crystalline structure against Sr content $x$ of Ba1-xSrxRuO3 at the ambient temperature and pressure was established in the present experiment as the nine-layer hexagonal for $x=0$, the four-layer hexagonal for $0.1 \leq x \leq 0.3$, the six-layer monoclinic for $0.5 \leq x \leq 0.7$ and perovskite for $x = 1.0$. The crystal is the mixture of the six-layer monoclinic and the four-layer hexagonal at around $x = 0.4$, and the mixture of the six-layer monoclinic and the perovskite at around $0.8 \leq x \leq 0.9$. At the phase boundaries, the volume per formula unit and the averaged interlayer distance show a discontinuous decrease with increasing Sr content. However, the changes within the phase are much smaller than those at the phase boundaries.
2009-09-15