In the present study we explore 4d and 5d perovskite oxides of alkaline-earth metals which find applications in both electronic and renewable energy devices. We investigate the atomic structure, electronic properties and defect formation energies of intrinsic vacancies as well as oxygen vacancy clustering in AZrO3 and AHfO3 (A = Ca, Sr and Ba) compounds. For this purpose all-electron Full-potential linear augmented plane-wave plus local-orbitals method within the framework of density functional theory has been employed. A detailed investigation of the electronic properties of aforementioned compounds is carried out by means of electronic band structures, density of states, charge densities and effective Bader Charges. The chemical stability diagrams of these compounds are also obtained from the total energy calculations which are used for determining the tolerance of the AZrO3 and AHfO3 compounds towards intrinsic vacancy defects under different growth conditions. Moreover, various cases of oxygen vacancy clustering are considered for predicting stable configuration of ordered oxygen vacancies and n-type conductivity in oxygen deficient AZrO3 and AHfO3 perovskite oxides. It is found that pristine AZrO3 and AHfO3 perovskite oxides are large band gap materials. We show that A site metal-atom vacancy is more likely 18 to be achieved during the synthesis of these materials and can be used for tuning p-type nature. On the other hand, the large band gap of all AZrO3 and AHfO3 perovskite oxides can be considerably reduced by introducing isolated oxygen vacancies in these materials. A systematic analysis of ordered oxygen vacancies in different layers of these materials allows us to predict that n-type conduction in AZrO3 and AHfO3 can be realized when oxygen vacancies cluster in the ZrO2 and HfO2 layers of these compounds, respectively. Our results provides useful information concerning the utilization of these materials in electronic, optical and energy devices.