2019 年 127 巻 3 号 p. 143-149
We have for the first time succeeded in the preparation of thin tabular crystals of K2O- and F-doped lanthanum silicate oxyapatite, which were grown by the high-temperature solution technique using KF as solvent. The crystals were characterized using microscopy, energy dispersive X-ray spectroscopy, electron probe microanalysis (EPMA), and X-ray diffractometry (XRD). The atomic compositions determined by EPMA showed the significant correlations among the numbers of atoms (N) for La, Si, and F. They were well expressed by the two linear equations of NLa = 17.52 − 1.426NSi and NF = −1.20 + 0.243NSi, which enabled us to derive the general formula of [La8.964+1.426xK0.850−0.035x]Σ9.814+1.391x[Si6−x□x]Σ6[O25.742+0.243xF0.258−0.243x]Σ26 (0 ≤ x ≤ 0.134), where x represents the amount of silicon deficiency denoted by □. Based on the single crystal XRD data, the crystal structure was refined for one of the grains, the chemical formula of which was eventually determined to be [La9.11K0.85]Σ9.96[Si5.90□0.10]Σ6[O25.77F0.23]Σ26 (x = 0.10). The K and F ions preferentially occupied, respectively, the La and O (channel oxide-ion) sites, with the silicon site being deficient by ca. 1.7%. Since the tabular crystals showed the well-developed {001} faces with relatively high aspect ratios, they could act as satisfactory templates for the preparation of the c-axis-oriented polycrystals.
