Ferroelectric behaviour of triglycine sulphate crystals containing low concentrations of metal ions near the transition temperature

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Abstract
Several ferroelectric properties of triglycine sulphate single crystals both pure and with different doping substitutions in the structure have been studied in the vicinity of the critical point Tc. The parameters engaged in the statistical dipolar theory of ferroelectrics are derived, from dielectric constant and hysteresis loop measurements, allowing a distinction between atomic and dipolar polarisation. The numerical values of the parameters obtained in this way for pure and doped crystals are compared. The internal biasing field is estimated using the data of the pyroelectric measurements. The basic pyroelectric material figure of merit is also calculated and its temperature dependence is reported. The temperature dependence of the coercive field has been measured and found to obey a power law Ec=A(Tc-T)s. The piezoelectric modulus and the electromechanical coupling coefficient have been also measured and their temperature dependence is investigated. The J-E characteristic in both the ferroelectric and the paraelectric phases is examined; variations in the behaviour according to the type of dopant are observed. The effect of polarising pure and doped TGS samples with a DC field of intensity 102 kV m-1 on measured properties is also examined.