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In the paper is demonstrated the use of positron lifetime spectroscopy (PLS) in a comparative study of the results in ferroelectrics. The first part is devoted to the application of PLS as a probe for measurements of ferroelectrics. In Triglycine Sulphate (TGS) (NH3CH2COOH)3H2SO4, Rochelle Salt (RS) NaKC4H4O64H2O and Potassium Dihydrogen Phosphate (KDP) KH2PO4 at different temperatures and gamma irradiation doses is established the existence of three positron lifetime components. This experimental results show that the second long lifetime component as a function of temperature in order-disorder ferroelectrics TGS, RS and KDP is due to the positron trapping in negatively charge defects of ferroelectric. The positron spectroscopy method is effective for measurements of extremely small defects and voids, which is important for the next exploitation period of the ferroelectrics. PLS measurements of ferroelectrics show that about the third lifetime component is due to the local formation of orhto-positronium state on the boundary between the domains. In the second part the PLS analysis has been applied for examination the electronic and defect structure in selected ferroelectrics materials. In gamma irradiated TGS positrons are trapped in the defect states of the oxygen ions of the two radicals CH2COO- and NH3CHCOO-. In RS positrons are trapped also in the defect states of the oxygen ions and OH groups.

Lattice defects containing hydrogen and helium in Pd have been studied by positron model calculations using Density Functional Theory [DFT] in its local density approximation [LDA] [1] implementation. A correlation between the positron lifetime, positron ground stage energy and number atoms of H and He has been established. It was found that the value of positron lifetime for perfect Pd lattice is 106 ps and for mono vacancy is 184 ps which corresponds to the experimental values.