The dehydration behavior of the experimentally produced Al0.5Fe05PO4 center dot 2.5H(2)O solid solution is assessed from thermogravimetrical (TG, differential thermogravimetric, DTG, and differential thermal analysis, DTA) and differential scanning calorimetry (DSC) analyses. The dehydration proceeded through a well-defined step at low temperatures (< 300 degrees C), which corresponds to the loss of 2.5 water molecules. The fluctuating dependence of the activation energies on fraction mass loss (alpha) for the dehydration reaction of Al0.5Fe0.5PO4 center dot 2.5H(2)O calculated through isoconversional methods (Ozawa and the Kissinger-Akahira-Sunose) indicates the existence of a complex multistep mechanism. The Avrami exponent value of 1.11 is indicative of one-dimensional growth as a phase boundary mechanism. The thermodynamic functions (Delta H*, Delta G*, and Delta S*) of the dehydration reaction calculated from the DSC technique are discussed for the first time.