The crystal structure and thermal expansion tensor of MgSO4–11D2O(meridianiite) determined by neutron powder diffraction
The crystal structure and thermal expansion tensor of MgSO4–11D2O(meridianiite) determined by neutron powder diffraction
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中子粉末衍射测定MgSO4–11D2O(子午线石)的晶体结构和热膨胀张量
DOI：
10.1007/s00269-008-0214-x
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发表时间：
2008
影响因子：
1.4
通讯作者：
K. Knight
中科院分区：
文献类型：
--
作者：
A. Fortes;I. Wood;K. Knight
摘要我们收集了 MgSO4·11D2O 在 4.2–250 K 温度范围内的高分辨率中子粉末衍射图。该晶体为三斜晶系、空间群
$$ \text{P} \bar{1} $$ (Z = 2) 其中 a = 6.72746(6) Å, b = 6.78141(6) Å, c = 17.31803(13) Å, α = 88.2062(6)°, β = 89.4473(8)°, γ = 62.6075(5)°，V = 701.140(6) Å3（4.2 K），a = 6.75081(3) Å，b = 6.81463(3) Å，c = 17.29241(6) Å，α = 88.1183(3)°， 250 K 时，β = 89.4808(3)°、γ = 62.6891(3)° 和 V = 706.450(3) Å3。在 4.2 和 250 K 时，结构分别细化为 wRp = 3.99 和 2.84%。晶格参数在中间范围内的温度依赖性已与修正的爱因斯坦振荡器模型相拟合，该模型用于获得热膨胀张量的系数。在所有温度下，体积热膨胀 αV 都远小于冰 Ih，甚至小于 MgSO4·7D2O（尽管两种硫酸盐的 ∂αV/∂T 非常相似）； MgSO4·11D2O 在 55 K 以下表现出负 αV（与 D2O 冰 Ih 中的 70 K 和 MgSO4·7D2O 中的 20 K 相比）讨论了膨胀张量主轴的大小和方向与主要结构元素之间的关系。
AbstractWe have collected high-resolution neutron powder diffraction patterns from MgSO4·11D2O over the temperature range 4.2–250 K. The crystal is triclinic, space-group
$$ \text{P} \bar{1} $$ (Z = 2) with a = 6.72746(6) Å, b = 6.78141(6) Å, c = 17.31803(13) Å, α = 88.2062(6)°, β = 89.4473(8)°, γ = 62.6075(5)°, and V = 701.140(6) Å3 at 4.2 K, and a = 6.75081(3) Å, b = 6.81463(3) Å, c = 17.29241(6) Å, α = 88.1183(3)°, β = 89.4808(3)°, γ = 62.6891(3)°, and V = 706.450(3) Å3 at 250 K. Structures were refined to wRp = 3.99 and 2.84% at 4.2 and 250 K, respectively. The temperature dependence of the lattice parameters over the intervening range have been fitted with a modified Einstein oscillator model which was used to obtain the coefficients of the thermal expansion tensor. The volume thermal expansion, αV, is considerably smaller than ice Ih at all temperatures, and smaller even than MgSO4·7D2O (although ∂αV/∂T is very similar for both sulfates); MgSO4·11D2O exhibits negative αV below 55 K (compared to 70 K in D2O ice Ih and 20 K in MgSO4·7D2O) The relationship between the magnitude and orientation of the principal axes of the expansion tensor and the main structural elements are discussed.