Hydroxyapatite whiskers were hydrothermally synthesized from amorphous

calcium phosphate, and their ionic conduction properties were investigated. The

whiskers obtained were assumed to be Ca-deficient hydroxyapatite with the composition, Ca9.18[HPO4]0.82[PO4]5.18[OH]1.18nH2O. Based upon the results of

complex impedance measurements, a multiple conduction mechanism was

suggested by the characteristic dependence of ionic conductivity upon temperature

at 250 to 600C. The conductivity increased to 5.0 x 10−9S/cm at 500C and then

decreased to 1.7 x 10−9S/cm as the temperature was further increased to 600C.

Since HPO4

2− ions were supposed to convert to P2O7

4− in about the same

temperature range where this particular change appeared, the increase in

conductivity up to 500C was assumed to be the result of an increase in the number

of mobile protons generated from HPO4

2−. The subsequent decrease in conductivity

seemed to be caused by a decrease in the number of protons; brought about by the

conversion of HPO4

2− to P2O7

4−, with the elimination of water.

Ionic Conduction Mechanism in Ca-Deficient Hydroxyapatite Whiskers. Y.Tanaka,

M.Nakamura, A.Nagai, T.Toyama, K.Yamashita: Materials Science and

Engineering B, 2009, 161[1-3], 115-9