Defect crystal structure of α-Na0.5–xR0.5+xF2+2x (R = Dy–Lu, Y) on X-Ray and electron diffraction data. II. Defect structure of the α-Na0.4R0.6F2.2 (R = Ho–Lu, Y) nanostructured crystals

The α-Na0.4R0.6F2.2 crystals (R = Ho–Lu, Y) were studied by X-ray diffraction analysis at 293 and 85 K. A unified cluster model of nanostructured crystals with a fluorite-type structure based on the polymorphism of KR3F10 (R = Er, Yb) was used to model their defect structure. The α-Na0.4R0.6F2.2 matrix component contained Na+ and R3+ in a ratio of 1 : 1. Part of the matrix anions was shifted from 8c to 32f position (sp. gr. Fm3m). Excess R3+ cations formed with Na+ octa-cubic clusters with nuclei in the form of cuboctahedra {F12} formed by interstitial anions at the 48i position. The α-Na0.4R0.6F2.2 cluster component was formed by octa-cubic clusters of type i. The electron diffraction method showed that the clusters had the shape of plates about 5 nm thick with superstructural ordering. Their structural model based on the K0.265Gd0.735F2.47 structure was proposed. For the first time, experimental confirmation of the affiliation of α-Na0.5–xR0.5+xF2+2x to nanostructured crystals was obtained by electron diffraction. When the temperature decreases from 293 to 85 K, the type of cluster component of the defect α-Na0.4R0.6F2.2 structure with R = Ho–Lu, and Y was not change. At 293 K, the boundary of the type change of the defect structure in the α-Na0.5–xR0.5+xF2+2x series was located between R = Dy (with the Z = 66 atomic number) and Ho (with Z = 67). When the temperature drops from 293 to 85 K, the position of the boundary was not change.