Self-organization processes and phase transitions in nanocrystalline hydroxyapatite according to exoemission data

Low-temperature (20–360°C) exoemission of negative charges from nanocrystalline hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ was studied. Thermal cycling and storage at 20°C were found to induce self-organization processes with charge separation and the formation of a negatively charged layer on the surface. The negative charge formed was long retained at elevated temperatures and only decreased during cooling in the temperature region of the structural transition, as is characteristic of thermoelectrets. No stable electrets formed in hydroxyapatite samples calcined at a high temperature (>800°C).