イットリウム固溶によるアパタイト焼結体の構造とイオン導電性変化

抄録

The electrical conduction of yttrium-substituted hydroxyapatite ceramics at high temperature was studied and the contribution of the proton to the high conduction of some sample among the above ceramics was examined as one of the potential proton-conductive materials for fuel cells of high temperature type.
Ac conductivities of the sintered apatite samples were measured by the two-probe method in the temperature range of 600 to 900°C, and the electromotive force for the water vapor cell consisting of yttrium bearing (Ca_9.35 Y_0.65 instead of Ca₁₀) apatite was measured.
From the results of X-ray diffraction and IR, the yttrium-substituted apatite ceramics may be represent as follows;
Ca_10-xY_x (PO₄) ₆ (OH) _2-x-2yO_x+2y_??__y.
In the vicinity of x=0.65, there were maximum electrical conductivity and minimum activation energy for conduction. The maximum value was by more than 100 times higher than that of the sintered hydroxyapatite. IR spectra for the sample x=1.0 indicated the absence of OH^- and the conduction by 0^2- was suggested. The conduction mechanism for the ceramics containing less than 0.5 of Y³⁺ was concluded to be similar to that of the sintered body of pure hydroxyapatite. The electromotive force of the apatite ceramics cell of x=0.65 was determined to be about 1500mV in case that the water vapor side was anionic, which showed the dominant proton conduction.