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首页> 外文期刊>Zeitschrift fur Naturforschung, B. A Journal of Chemical Sciences >High-pressure investigations of lanthanoid oxoarsenates: I. Single crystals of scheelite-type Ln[AsO4] phases with Ln = La-Nd from monazite-type precursors
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High-pressure investigations of lanthanoid oxoarsenates: I. Single crystals of scheelite-type Ln[AsO4] phases with Ln = La-Nd from monazite-type precursors

机译：镧系元素含氧砷酸盐的高压研究：I.独居石型前体中白钨矿型Ln [AsO4]相的单晶，Ln = La-Nd

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摘要

Transparent single crystals of the scheelite-type Ln[AsO4] phases with Ln = La-Nd are obtained by the pressure-induced monazite-to-scheelite type phase transition in a Walker-type module under high-pressure and high-temperature conditions of 11 GPa at 1100-1300 degrees C. Coinciding with this transition, there is an increase in density and a reduction in molar volume of about 4.5 % for the scheelite-type phases (tetragonal, I4(1)/a) for La[AsO4] (a = 516.92(4), c = 1186.1(9) pm), Ce[AsO4] (a = 514.60(1), c = 1175.44(2) pm), Pr[AsO4] (a = 512.63(4), c = 1168.25(9) pm), and Nd[AsO4] (a = 510.46(4), c = 1160.32(11) pm) as compared to the well-known monazite-type phases (monoclinic, P2(1)). Surprisingly enough, the scheelite-type oxoarsenates(V) exhibit a lower coordination number for the Ln(3+) cations (CN = 8 versus CN = 8 + 1), whereas the isolated tetrahedral [AsO4](3-) anions (d(As-O) = 168.9-169.3 pm for the scheelites as compared to d(As-O) = 167.1-169.9 pm for the monazites) remain almost unchanged. So the densification must occur because of the loss of two edge-connections of the involved [LnO(8+1)](15-) polyhedra with the [AsO4](3-) tetrahedra in the monazite-resulting in exclusively vertex connected [LnO(8)](13-) and [AsO4](3-) units in the scheelite-type structure.
机译：Ln = La-Nd的白钨矿型Ln [AsO4]相透明单晶是通过在Walker型组件中在高压和高温条件下通过压力诱导的独居石-白钨矿型相变而获得的。 1100-1300摄氏度时为11 GPa。与此转变同时，La [AsO4]的白钨矿型相（四方晶系，I4（1）/ a）的密度增加，摩尔体积减少约4.5％。 ]（a = 516.92（4），c = 1186.1（9）pm），Ce [AsO4]（a = 514.60（1），c = 1175.44（2）pm），Pr [AsO4]（a = 512.63（4） ，c = 1168.25（9）pm）和Nd [AsO4]（a = 510.46（4），c = 1160.32（11）pm），与著名的独居石型相（单斜晶系，P2（1）/ n）。令人惊讶的是，白钨矿型含氧砷酸盐（V）对Ln（3+）阳离子具有较低的配位数（CN = 8对CN = 8 +1），而分离的四面体[AsO4]（3-）阴离子（d scheelite的（As-O）= 168.9-169.3 pm，独居石的d（As-O）= 167.1-169.9 pm几乎保持不变。因此，由于在独居石中[LnO（8 + 1）]（15-）多面体与[AsO4]（3-）四面体的两个边沿连接的损失而导致了致密化，从而导致了唯一的顶点连接[白钨矿型结构中的LnO（8）]（13-）和[AsO4]（3-）单元。

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