Zircon-type PrVO4 was shown recently to be a mixed ionic-electronic conductor. Electronic transport was attributed to electron-hopping between Pr3+/Pr4+ cations, with Pr4+ cations in the lattice presumably compensated by formation of interstitial oxygen ions. Although oxygen-ionic transport in LnVO4 is often assumed to occur via interstitial oxygen diffusion, there is no firm experimental evidence of this. Another phenomenon characteristic for LnVO4 is protonic transport in wet atmospheres. Again, the mechanism of proton incorporation into zircon-type structure was not studied so far. In the proposed experiment, we would like to collect ND patterns for Pr1-xCaxVO4 (x = 0-0.05), hydrated and anhydrous, to determine the localization of structural defects (oxygen ions/vacancies and protons) and provide an insight on mechanisms of oxygen-ionic and protonic transport in these materials.