الفهرس 
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Abstract
,
A series of double sulphate and double selenate single crystals
hasbeen grown by the slow evaporation method from concentrated
aqueous solutions containing the initial salts at the required
stoichiometricratios. Doped samples were prepared by the addition of
Cr3+ ionsto the growth solution. The concentration of Cr3+ ions was
determinedby a chromatographic method.
Characterizationsof the prepared crystals have been made from
the studiesof x-ray diffraction, differential thermal analysis (DTA),
specificheat under constant pressure Cp(T) measurements, as well as
the measurementsof electrical properties over the temperature range
from4.2 K to 500 K.
The effect of both doping with Cr3+ ions and y-radiation on the
thermaland electrical properties of the pure crystals have been also
investigated.
The X-ray diffraction analysis showed the existence of the
crystallinestate of the samples.
Thedifferential thermal analysis (DTA) showed the existence of
a discontinuous ferroelectric-paraelectric phase transition at
Tc= 100Kfor NaNH4So4.2H20 crystals.