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首页> 外文期刊>Journal of Materials Research >Thermochemistry of the alkali rare-earth double phosphates, A_3RE(PO_4)_2
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Thermochemistry of the alkali rare-earth double phosphates, A_3RE(PO_4)_2

机译：碱土金属双磷酸盐A_3RE（PO_4）_2的热化学

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摘要

The formation enthalpies for alkali rare-earth compounds of the type K_3RE(PO_4)_2 where RE = Sc, Y, Lu, Er, Ho, Dy, Gd, Nd, or Ce and for A_3Lu(PO_4)_2 compounds with A = K, Rb, or Cs were determined using high-temperature oxide-melt solution calorimetry. Structural phase transitions were observed and characterized using differential scanning calorimetry and high-temperature x-ray diffraction. The formation enthalpy of the K_3RE(PO_4)_2 phases from oxides becomes more exothermic with increasing rare-earth radius for the K_3RE(PO_4)_2 series and with increasing alkali radius for the A_3Lu(PO_4)_2 compounds. The K_3RE(PO_4)_2 phases are stable with respect to anhydrous K_3PO_4 and REPO_4. The monoclinic K_3RE(PO_4)_2 compounds undergo a reversible phase transition to a hexagonal (glaserite-type) structure with a phase transition temperature that increases from -99 to 1197 deg C with increasing RE ionic radius going from Lu to Ce.
机译：K_3RE（PO_4）_2类型的碱土金属化合物（RE = Sc，Y，Lu，Er，Ho，Dy，Gd，Nd或Ce的形成焓和A = K的A_3Lu（PO_4）_2化合物的形成焓，Rb或Cs使用高温氧化物熔体溶液量热法测定。使用差示扫描量热法和高温X射线衍射观察并表征结构相变。氧化物的K_3RE（PO_4）_2相的形成焓随着K_3RE（PO_4）_2系列的稀土半径增加和A_3Lu（PO_4）_2化合物的碱半径增大而放热。 K_3RE（PO_4）_2相相对于无水K_3PO_4和REPO_4是稳定的。单斜K_3RE（PO_4）_2化合物经历可逆相变，形成六方晶（玻璃沸石型）结构，相变温度从-99升高到1197℃，随着RE离子半径从Lu到Ce的增加。

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