Structures and isomorphous substitutions in Cs-Mg-Beryl and Cs-rich beryllian indialite formed in a flux medium

Mikhailov M.A.; Rozhdestvenskaya I.V.; Bannova I.I.

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Structures and isomorphous substitutions in Cs-Mg-Beryl and Cs-rich beryllian indialite formed in a flux medium

机译：通量介质中形成的Cs-Mg-铍和富Cs铍辉石的结构和同构取代

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The crystal structures of isostructural compounds-Cs-Mg-beryl (Al _(1.68)Mg_(0.31)Fe_(0.01)) (Be_(2.68)Si _(0.02)A_(l0.26-0.04))Si_(6.00)O_(18). Cs _(0.07) (a = 9.2359(9) ?, c = 9.204(1) ?) and the Cs variety of beryllian indi-alite (Mg_(1.90)Fe_(0.10))(Be _(1.02)Al_(1.98)) (Al_(0.30)Si_(5.70))O _(18). Na_(0.02)Cs_(0.16) (a = 9.598(3) ?, c = 9.284(3) ?)-were refined. These compounds were formed in the Al _2Be_3Si_6O_(18)-Mg,Ca/F,Cl flux system in the presence of cesium chloride. The main structural features of these compounds were determined. It was found that the iso-morphous incorporation of Cs~+ cations into anhydrous beryl proceeds according to the simple 'vacancy' scheme Be_(T2) → 2(Cs~+)_R +-_(T2), whereas the complex heterovalent substitution _9Si_(T1) + Al_(T2) → _9Al_(T1) + Be_(T2) + 9(Cs, Na)_R is observed in Cs-rich beryllian indialite under anhydrous conditions; i.e., no vacancies are formed in the tetrahedral framework of the latter structure. In Cs-Mg-beryl, an increase in the average bond lengths in the M octahedron and in the interring T2 tetrahedron leads to an increase in the unit-cell parameters a and c. In Cs-rich beryllian indialite, a slight increase in the M-O bond length and a decrease in T2-O bond length cause a slight increase in the parameter a and a decrease in the parameter c The Cs~+ cat-ions are incorporated into the channels of both compounds at the height of the interring M-T2 layer (like K~+ cations), whereas the Na ~+ cation is incorporated inside the Si_6O_(18) ring. The dT1 value suggests that the change in the composition caused by the incorporation of Cs~+ cations leads to the incongruent melting of beryllian indialite.

机译：同构化合物-Cs-Mg-铍基（Al _（1.68）Mg_（0.31）Fe_（0.01））（Be_（2.68）Si _（0.02）A_（l0.26-0.04））Si_（6.00）的晶体结构O_（18）。 Cs _（0.07）（a = 9.2359（9）？，c = 9.204（1）？）和Besylian英莱石的Cs变种（Mg_（1.90）Fe_（0.10））（Be _（1.02）Al_（1.98 ））（Al_（0.30）Si_（5.70））O _（18）。精制Na_（0.02）Cs_（0.16）（a = 9.598（3）？，c = 9.284（3）？）。这些化合物是在氯化铯存在下于Al _2Be_3Si_6O_（18）-Mg，Ca / F，Cl助熔剂体系中形成的。确定了这些化合物的主要结构特征。结果发现，Cs〜+阳离子同构结合到无水绿柱石中是根据简单的“空位”方案Be_（T2）→2（Cs〜+）_ R + -_（T2）进行的，而复杂的杂价取代在无水条件下，在富含Cs的铍绿辉石中观察到_9Si_（T1）+ Al_（T2）→_9Al_（T1）+ Be_（T2）+ 9（Cs，Na）_R;即，在后一结构的四面体框架中没有形成空位。在Cs-Mg-铍基中，M八面体和T2环四面体中平均键长的增加导致单位晶胞参数a和c的增加。在富含Cs的铍辉石岩中，MO键长度的略微增加和T2-O键长度的减小会导致参数a略有增加，而参数c则有所下降。两种化合物都在环M-T2层的高度处形成通道（如K〜+阳离子），而Na〜+阳离子被掺入Si_6O_（18）环内。 dT1值表明由Cs〜+阳离子的掺入引起的成分变化导致铍辉石的熔融不一致。

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《Crystallography reports》 |2012年第6期|共9页
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Mikhailov M.A.; Rozhdestvenskaya I.V.; Bannova I.I.;
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Structures and isomorphous substitutions in Cs-Mg-Beryl and Cs-rich beryllian indialite formed in a flux medium

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