Syamaprasad, U; Dr.Girijavallabhan,C P(Cochin University of Science And Technology, December , 1981)
[+]
[-]
Abstract:
The thesis aims to present the results of the
experimental investigations on the electrical properties like
electrical conductivity, dielectric constant and ionic thermo~
currents in certain ammonium containing ferroelectric crystals
viz. LiNH4SO4, (NH4)2SO4 and (NH4)5H(SO4)2. Special attention
has been paid in revealing the mechanisms of electrical conduction
in the various phases of these crystals and those asso~
ciated with the different phase transitions occurring in them,
by making studies on doped, quenched and deuterated crystals.
The report on the observation of two new phase transitions in
(NH4) S O2 and of a similar one in ( NH4 ) H (2SO4 ) are included. The relaxation mechanisms of the impurity-vacancy complexes and the space charge phenomena in pure and doped crystals of LiNH4SO4 and (NH4)2SO4 and the observation of a new type of ionic thermo-current viz. Protonic Thermo-Current (PTC) in these crystals are also presented here.
Description:
Department of Physics, Cochin University of Science and Technology
Santhakumari, N C; Dr.Girijavallabhan,C P(Cochin University Of Science And Technology, February 15, 1992)
[+]
[-]
Abstract:
Solid electrolytes for applications like
chemical sensing, energy storage, and conversion have been
actively investigated and developed since the early
sixties. Although of immense potential, solid state
protonic conductors have been ignored in comparison with
the great interest that has been shown to other ionic
conductors like lithium and silver ion conductors. The
non-availability of good, stable protonic conductors could
be partly the reason for this situation. Although organic
solids are better known for their electrical insulating
character, ionic conductors of organic origin constitute a
recent addition to the class of ionic conductors.
However, detailed studies (N1 such conductors are scarce.
Also the last decade has witnessed an unprecedented boom
in research on organic "conducting polymers". These newly
devised materials show conductivity spanning from
insulator to metallic regimes, which can be manipulated by
appropriate chemical treatment. They find applications in
devices ranging from rechargeable batteries to "smart
windows".
This thesis mainly deals with the synthesis and
investigations on the electrical properties of (i) certain organbc protonic conductors derived from ethylenediamine
and (ii) substituted polyanilines
Description:
Department
of Physics, Cochin University of Science and Technology
Godfrey,Louis; Jacob, Philip(Department of Physics, 1994)
[+]
[-]
Abstract:
The thesis investigated the elastic properties and phase transitions in selected mixed sulphate crystals – Lithium Hydrazinium Sulphate [LiN2H2SO4], Lithium Ammonium Sulphate [LiNH4SO4] and Lithium Potassium Sulphate [LiKSO4] – using ultrasonic technique. The pulse echo overlap technique has been used for measuring ultrasonic velocity and its dependence on temperature along different directions with waves of longitudinal and transverse polarizations. Two major numerical techniques and the corresponding computer programs developed as part of present work are presented in this thesis. All the 9 elastic constants of LHS are determined accurately from ultrasonic measurements and applying misorientation correction refines the constants. Ultrasonic measurements are performed in LAS to determine the elastic constants and to study the low temperature phase transitions. Temperature variation studies of elastic constant of LAS are performed for 6 different modes of propagation for heating and cooling at low temperatures. All the 5 independent elastic constants of LPS is determined using ultrasonic measurements. It is concluded that LPS crystal does not undergo a phase transition near this temperature. A comparison of the three crystals studied shows that LPS has maximum number of phase transitions and LHS has the least number. It is interesting to note that LPS has the simplest formula unit among the three. There is considerable scope for the future work on these crystals and others belonging to the sulphate family.