Particles of carbonated barium-calcium hydroxyapatite solid Solutions (BaCaHap) with different Ba/(Ba + Ca) atomic ratios were prepared by a wet method at 100 degrees C and characterized by various means, The crystal phases and qructures of the products strongly depended on the composition of the starting solution, that is, the Ba/(Ba+Ca) atomic ratio (vertical bar X(Ba)vertical bar) and H3PO4 concentration ([H3PO4]) in the solution. BaCaHap with X-Ba <= 0.43 could be prepared at vertical bar X(Ba)vertical bar = 0.7 by changing vertical bar H(3)PO(4)vertical bar bill could never be obtained at [X-Ba] = 0.8-0.95 regardless of vertical bar H(3)PO(4)vertical bar. The carbonated calcium hydroxyapatite particles prepared at vertical bar X(Ba)vertical bar = 0 were line and short rod-shaped particles (ca. 14 x 84 nm). With increasing vertical bar X(Ba)vertical bar from 0 to 0.8. the particles obtained became large spherical agglomerates. The carbonated barium hydroxyapatite particles formed at vertical bar X(Ba)vertical bar = 1 were long rod-shaped agglomerates (ca. 0.2 x 2 mu m) of fine primary particles. The amount of CO2 adsorbed irreversibly on a series of BaCaHaps showed a Minimum at Ma + Ca)/(P + (7) atomic ratio of around 1.56 which agreed well with the minimum cation/P ratio obtained for the other hydroxyapatites was already reported. (c) 2005 Elsevier Inc. All rights reserved.