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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Phase transition in K3Na(MoO4)(2) and determination of the twinned structures of K3Na(MoO4)(2) and K2.5Na1.5(MoO4)(2) at room temperature
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Phase transition in K3Na(MoO4)(2) and determination of the twinned structures of K3Na(MoO4)(2) and K2.5Na1.5(MoO4)(2) at room temperature

机译：室温下K3Na（MoO4）（2）的相变和K3Na（MoO4）（2）和K2.5Na1.5（MoO4）（2）孪生结构的确定

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摘要

The room-temperature phases of sodium potassium molybdates K3Na(MoO4)(2) and K2.5Na1.5(MoO4)(2) are isostructural with the monoclinic low-temperature phases of K3Na(SeO4)(2) and K3Na(CrO4)(2), which are twinned distorted glaserite structures. In the molybdates there are two crystallographically independent potassiums and their environment slightly differs from those in K3Na(SeO4)(2) and K3Na(CrO4)(2). The excessive Na in K2.5Na1.5(MoO4)(2) occupies the position of the more firmly bound potassium. A reversible phase transition at 513 K was discovered in K3Na(MoO4)(2) by DSC (differential scanning calorimetry), but no such transition in K2.5Na1.5(MoO4)(2) was detected. Both samples used in the diffractometer experiment were found to be composed of six domains being related by twinning operations of the point group 6. The twinning may be considered as a combination of a merohedral and a pseudo-merohedral twinning with two-and threefold rotations as twinning operations, respectively. However, a reversible domain switching, which is observable in the related ferroelastic crystals of K3Na(SeO4)(2) and K3Na(CrO4)(2), was not observed either in K3Na(MoO4)(2) or in K2.5Na1.5(MoO4)(2), either due to semitransparency of the samples or high ferroelastic distortion. This distortion is manifested by the values of the atomic displacement vectors which are about twice as large as those in the selenate or the chromate.
机译：钼酸钠钾K3Na（MoO4）（2）和K2.5Na1.5（MoO4）（2）的室温相与K3Na（SeO4）（2）和K3Na（CrO4）的单斜低温相同构（2），它们是孪晶畸变的玻璃结构。在钼酸盐中，有两个晶体学上独立的钾，其环境与K3Na（SeO4）（2）和K3Na（CrO4）（2）略有不同。 K2.5Na1.5（MoO4）（2）中过量的Na占据了结合更牢固的钾的位置。通过DSC（差示扫描量热法）在K3Na（MoO4）（2）中发现了在513 K处可逆的相变，但在K2.5Na1.5（MoO4）（2）中未检测到这种相变。发现在衍射仪实验中使用的两个样品均由与点组6的孪生操作相关的六个域组成。该孪生可被视为具有2和3倍旋转的多面体和拟多面体孪生的组合，例如孪生操作。但是，在K3Na（MoO4）（2）或K2.5Na1中均未观察到可逆的域转换，这在相关的K3Na（SeO4）（2）和K3Na（CrO4）（2）的铁弹性晶体中可见。 5（MoO4）（2），可能是由于样品的半透明性或高铁弹性变形引起的。这种变形通过原子位移矢量的值来体现，该值约为硒酸盐或铬酸盐中原子位移矢量的两倍。

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