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A novel gallium-doped -tricalcium phosphate (-TCP) ceramics with rhombohedral structure (R3c space group) can be obtained by the addition of a Ga precursor in the typical reaction protocols used for the preparation of -TCP. It was found, from the refinement of their XRD patterns, that the incorporation of Ga in the -TCP network occurs by substitution of one of the five calcium sites, while occupation of another Ca site decreases in inverse proportion to the gallium content in the structure. A decrease of the unit cell volume is observed with increasing gallium content, together with improved mechanical properties. Indeed, the compressive strength of these new bioceramics is enhanced in direct proportion of the Ga content, up to a 2.6-fold increase as compared to pure -TCP.

Several substituted â-tricalcium phosphates have been prepared with different cations (monovalent, divalent and trivalent) and at various levels of substitution. Structural investigations have proved that fewer than ~10% wt substitution, the substituted compounds are isostructural to â- TCP, leading to solid solutions. These samples have been characterized by infrared and Raman spectroscopies. The vibrational spectra show mainly the bands related to the vibrations of PO43- tetrahedrons present in the structure. As Raman scattering and infrared absorption are local probes, the bands are sensitive to the local environment of the distinct tetrahedrons, related to the site of substitution and to the nature of the cations.

The infrared and Raman spectra of Na substituted β-TCP are presented for various levels of substitution. The influence of Na content on main vibrational modes appears significant and among them the ν1 symmetric stretching band is very sensitive to PO4 3- tetrahedrons environment. Thus, this mode was particularly investigated and has been decomposed using Lorentzian shapes components. We assigned the calculated components to the different types of PO4 3- tetrahedrons present in the crystalline structure.