Fast Oxide Ion Conduction Due to Carbonate Substitution in Hydroxyapatite

Abstract

To provide ceramic electrets with superior biocompatibility and controlled surface energy utilizing long‐distance ionic conduction under a DC electric field, the conduction property of B‐type carbonated apatite (CA) ceramics with various carbonate content was investigated by complex impedance measurements and a concentration cell technique. Infrared spectroscopy and X‐ray diffractometry indicated that B‐type CA with the composition of Ca10−xNa2x/3(PO4)6−x(CO3)x(H2O)x(OH)2−x/3 (x=ca. 0.87, 1.14, and 1.78, which is identified as CA1, CA2, and CA3, respectively) was prepared. The carbonate content significantly influenced the ionic conductivity (σ) of the obtained CA, which drastically increased from 10−8 to 10−3 S/cm (700°C) in the range between x=0.87 and 1.14. Detection of stable electromotive forces in an oxygen concentration cell using CA1 and CA2 electrolyte (cathode: 5N‐graded oxygen gas, anode: nitrogen‐balanced 5%–95% oxygen gas) provided strong evidence for oxide ion conduction in B‐type CA. Comparison of the obtained electromotive forces (EMFex) with the theoretical ones (EMFth) suggested that the transference numbers for oxide ion conduction in CA1 and CA2 were 0.17 and 1.01, respectively. This result demonstrated that a substitution ratio in excess of one‐sixth phosphate ions to carbonate ions (x=1) converted the B‐type CA from a proton conductor into an oxide ion conductor.

The illumination intensity and applied bias voltage on dielectric properties of au/polyvinyl alcohol (Co, Zn‐doped)/n‐Si Schottky barrier diodes

“…We have recently reported the possibility of an ionic conduction in β‐TCP through thermally stimulated depolarization current measurements in the polarization of CP ceramics 16. We have also very recently demonstrated pure O 2− conduction in CAp5 using the thermodynamic method of oxygen concentration cells 32. Based on these results, we presently assume the existence of O 2− conduction even in CAp1 and CAp2, which result in higher E a C values despite a higher σ for the family of CAp.…”

Understanding bioactivity and polarizability of hydroxyapatite doped with tungsten

“…This result indicates that β‐TCP phase primarily contributed to the polarization charge in 0.5% doped HAp sample. Polarization of doped β‐TCP was assumed to be due to the migration of Ca 2+ or O 2− ion33, 34 in contrast to H + migration in HAp phase. As the lattice structure of β‐TCP contains some inherent Ca 2+ vacancies, the conduction of Ca 2+ ion by vacancy mechanism is possible.…”

Enhanced high-temperature electrical response of hydroxyapatite upon grain size refinement

“…O 2À ions would act as electrostatic barrier for migration of OH À ions along conductive columns and decrease overall conductivity [17]. If conductivity of GI for M-HA and S-HA is assumed to behave as conductive O 2À ions mechanism (activation energy 1.5 eV [16]), the values of M-HA and S-HA GI conductivity would be rather enhanced and probably higher than that of N-HA sample since the migration of O 2À ions would carry doubled charge comparing to that of single-charged OH À conductivity [18]. Since this situation was not observed, O 2À ions could exist in crystal lattice of HA but do not behave as main charge carriers.…”