钙钛矿Na1.64 K 0.36 Ca（CO3）2的强烈调制孪晶结构
Incommensurately modulated twin structure of nyerereite Na1.64K0.36Ca(CO3)2
摘要：
在（3+1）D对称群Cmcm（α00）00 s中首次确定了奈米石Na_（1.64）K_（0.36）Ca（CO_3）_2的强烈调制孪晶结构，调制矢量q = 0.383a ~*。晶胞参数a = 5.062（1），b = 8.790（1），c = 12.744（1）Ω。三个正交分量通过围绕[001]的三次旋转而相关。不连续的cernel函数被用来描述占据调制的Ca和一些CO 3基团。强位移调制的氧原子在顶点的这种CO 3组描述使用x-谐波在垛口间隔。Na、K原子占据混合位置，其占据调制可用互补调和函数和垛口两种方式描述。并将其结构与无钾Na_2Ca（CO_3）_2的调变结构和γ-Na_2CO_3的调变结构进行了比较。
英文摘要：
Incommensurately modulated twin structure of nyerereite Na1.64K0.36Ca(CO3)2 has been first determined in the (3+1)D symmetry group Cmcm(α00)00s with modulation vector q = 0.383a*. Unit-cell values are a = 5.062(1), b = 8.790(1), c = 12.744(1) Å. Three orthorhombic components are related by threefold rotation about [001]. Discontinuous crenel functions are used to describe occupation modulation of Ca and some CO3 groups. Strong displacive modulation of the oxygen atoms in vertexes of such CO3 groups is described using x-harmonics in crenel intervals. The Na, K atoms occupy mixed sites whose occupation modulation is described by two ways using either complementary harmonic functions or crenels. The nyerereite structure has been compared both with commensurately modulated structure of K-free Na2Ca(CO3)2 and with widely known incommensurately modulated structure of γ-Na2CO3.
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