Proton transport polarization and depolarization of hydroxyapatite ceramics

Abstract

Polarization of sintered hydroxyapatite (HAp) ceramics by application of an external dc field at higher temperature was analyzed by thermally stimulated depolarization current (TSDC) measurements. The mechanisms for the polarization and depolarization of HAp were discussed in relation to the instability of the protons in the hydroxide groups. The TSDC spectra consisted of broad peaks, while the ferroelectric substances such as the BaTiO3 ceramics exhibited a sharp peak. Although the maximum current density of 7.87 nA cm−2 for the HAp polarized at 400 °C under 1.0 kV cm−1 was approximately 1/12 lower than that of BaTiO3, the polarization charge of 14.9 μC cm−2 was almost twice as large as that of BaTiO3. Considering the activation energy of 0.72–0.89 eV for the depolarization, it was revealed that the polarization of HAp was ascribed to the migration of protons in the columnar OH− channels with a micrometer-order distance. It was also found that the polarization charge was large and long enough to enhance the biological reactivity of HAp ceramics for biomedical implants.

Компьютерные Исследования Наноструктур Гидроксиапатита, Их Особенности И Свойства

“…Note, that similar polarization (in absolute values) was estimated on the order of ~ 0.005 C/m 2 for various type of HAP NPs [30] (see Table 3), the other measured data 0.072 C/m 2 is close to the value for HAP crystal structure ~ 0.1 C/m 2 estimated in works [13-15, 28, 29], and computed for minimal sized HAP cluster (see Table 4) [30]. These data are comparable with the biggest known measured value 0.149 C/m 2 by Nakamura [12], and it is only twice lower in average. Here we should make some remarks on the results, which were obtained in work [61].…”

“…Here we should make some remarks on the results, which were obtained in work [61]. There a very small surface charge (0.000033 C/m 2 ) was registered under the following poling conditions: Ep = 400 V/mm ~ 400 kV/m, Tp = 350 C, and tp = 60 min, which is two orders lower than the above values [30,43,60] and almost four orders of magnitude smaller than the values of 0.1-0.149 C/m 2 , (under similar poling condition Ep = 100 kV/m, Tp = 400 °C, tp ~ 1 hour) [12]. The latter result was obtained by thermally stimulated depolarization current (TSDC) measurements, and is comparable with other above estimations [13][14][15][28][29][30].…”

“…It has specific structural features that define its basic physical properties, charge distribution and surface electric potential, which have especially important role for the living cells adhesion and proliferation [1][2][3]. The specific feature of HAP is that it has a selected direction of the formation of hydroxyl OH groups (inner OH-channels) along the c axis, which allows the transfer of protons along this axis under special conditions [4][5][6][7][8][9][10][11][12][13][14][15]. Special interest here is connected with the physical properties of the nanosized HAP clusters [12][13][14][15][16][17][18][19][20][21].…”

“…9. Scheme of HAP NP energy band structure and its shift by the internal electric field Eel arising, due to the polarization P of the HAP cluster: a) in vacuum, b) on negative substrate (partly modified and printed with permission from IOP Publishing, LTD Copyright Clearance Center [30] It is necessary to note that the polarization values calculated in this model are not so large (the most important data is at the level ~ 0.5 C/cm 2 that is less than the known data for HAP polarized by an applied electric field [12]), but this polarization is essential for this HAP NP structure, because it appears and exists as spontaneous (self-induced or self-organized) polarization similar to the ordered dipole momentum as in ferroelectrics (see also in [43]). This polarization -as revealed by the surface charges on HAP NPs -leads to the existence of an electric field inside the cluster.…”

Change in the morphology of hydroxyapatite nanocrystals in the presence of bioaffinitive polymeric species under the application of electrical field

“…Thus, polarization of HAP-HYA composite is predominated by HAP, as in the case of the composite system with GLT [7]. Polarization mechanism of HAP in the case of poling the sintered HAP is known to be the self-organization of the polaron H C -O 2K as a consequence of the successive proton migration into the proton vacancy around O 2K [9]. The possibility that the polarization of OH K parallel to the c-axis is promoted was suggested in the HAP-GLT composite [7].…”