Bioapatite, the major constituent of mineralized tissues in mammalian bones and teeth, has been modeled to the hexagonal hydroxyapatite phase. Monoclinic hydroxyapatite, synthesized before only at very high temperature, is the thermodynamically most stable phase and is expected to exist also in hard tissues. In this work, hydroxyapatite nanobelts are produced by hydrolysis of brushite crystals and are identified to be the monoclinic phase based on electron microscopy and electron diffraction techniques. This is the first report of fabricating monoclinic hydroxyapatite crystals at low temperature. As the structural differences between hexagonal or monoclinic hydroxyapatite are very subtle, the success of this characterization also shows the great potential of electron microscopy and electron diffraction techniques for precise phase identification.

The search for new superconducting materials has been spurred on by the discovery of iron-based superconductors whose structure and composition is qualitatively different from the cuprates. The study of one such material, KxFe2−ySe2 with a critical temperature of 32 K, is made more difficult by the fact that it separates into two phases—a dominant antiferromagnetic insulating phase K2Fe4Se5, and a minority superconducting phase whose precise structure is as yet unclear. Here we perform electrical and magnetization measurements, scanning electron microscopy and microanalysis, X-ray diffraction and scanning tunnelling microscopy on KxFe2−ySe2 crystals prepared under different quenching processes to better understand the relationship between its microstructure and its superconducting phase. We identify a three-dimensional network of superconducting filaments within this material and present evidence to suggest that the superconducting phase consists of a single Fe vacancy for every eight Fe-sites arranged in a √8 x √10 parallelogram structure.