The Ba2+-2H(+) ion exchange process has been studied, and exchange isotherms and titration curves have been obtained at 25.0, 40.0 and 55.0 degrees C (+/-0.1 degrees C). The gamma-Ti(Ba0.5HPO4)(PO4).1.5H(2)O phase was formed by using BaCl2, and HCl solutions. Equilibrium constants, free energy, enthalpy and entropy of the exchange reaction were determined. The barium half-exchanged phase loses water stepwise at progressively higher temperatures until it becomes anhydrous. At 900 degrees C a mixture of two crystalline solid phases (BaTiP2O8 and alpha-TiP2O7) is obtained. The results are compared with those obtained by decomposition of the gamma-Ti(Ca0.37H1.25PO4)(PO4).3.5H(2)O phase at 900 degrees C, which produces a mixture of CaTi4(PO4)(6), Ca-3(PO4)(2) and alpha-TiP2O7 phases.