p-Phenylenediamine dihydroperchlorate, $C_6H_4N_2H_4{cdot}2HC1O_4$, crystallizes in space group $P={1}$ with $a=4.79{pm}0.02,;b=9.03{pm}0.02,;c=7.12{pm}0.03{AA},;{alpha}=109.4{pm}0.2,;{eta}=79.6{pm}0.2,;r=104.6{pm}0.2^{circ},;Z=1$. The structure has been solved by the Patterson and Fourier methods. The refinement by block-diagonal least-squares cycles gives R = 0.13 for 387 observed reflexions collected on equi-inclination Weissenberg photographs with CuK${alpha}$ radiation. There are two different types of five hydrogen bonds. The first type consists of one trifurcated N${cdot}{cdot}{cdot}$O hydrogen bond and the second of two normal N${cdot}{cdot}{cdot}$O hydrogen bonds, both of which exist between the amino group and the perchlorate, groups. A p-phenylenediamine group is approximately planar within an experimental error and bonded to twelve perchlorates: ten perchlorates forming hydrogen bonds and two being contacted with the van der Waals forces. A perchlorate group is surrounded by six p-phenylenediamines and four perchlorates; among the six p-phenylenediamines, five of them are hydrogen-bonded, and the rest contacted with the van der Waals force.ce anaysis of our samples and investigated the variarions in the values of parameters obtained through fitting the theoretical impedance to the experimental impedance. The characters of the dielectric constant and the impedance showed abnormal variations for the 0.2 at K-doped NSBN ceramics, which we were able to interpret in terms of the variations in the number A-site vacancies with the K doping ratio. From these results, A-site vacancies are thought to be space charges that influence the ferroelectric properties of NSBN ceramics.