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| Abstract: | Four distinct peaks are observed at 140, -26, -132 and -140°C in the sigma x* against T-1 plot between 200 and - 196°C for (NH4)3H(SO4)2, corresponding to four different phase transitions of which the one at -26°C is reported here for the first time. Data on doped samples reveal the charge transport mechanism in the crystal. |
| URI: | http://dyuthi.cusat.ac.in/purl/2424 |
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| Dyuthi-P0278.pdf | (326.3Kb) |
| Abstract: | Measurements of dc conductivity and dielectric constant show that deuteration causes an upward shift of the high temperature phase transition point from 186.5 to 191°C and a downward shift of the low temperature transition point from 10 to -1.5°C in LiNH4SO4. Mechanisms of phase transitions and of electrical transport in the crystal are discussed. |
| URI: | http://dyuthi.cusat.ac.in/purl/2503 |
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| Dyuthi-P0280.pdf | (275.7Kb) |
| Abstract: | Anomalous variations of d.c. electrical conductivity with temperature are observed in ammonium sulphate single crystals, suggesting a possible phase transition at 150°C. Measurements of thermally stimulated current also support these results. The mechanism of electrical conduction is explained on the basis of studies made on doped and quenched crystals. |
| URI: | http://dyuthi.cusat.ac.in/purl/2488 |
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| Dyuthi-P0277.pdf | (383.4Kb) |
| 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 |
| URI: | http://dyuthi.cusat.ac.in/purl/3643 |
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| Dyuthi-T1620.pdf | (15.83Mb) |
| Abstract: | Results of axiswise measurements of the electrical conductivity (dc and ac) and dielectric constant of NH4H2PO4 confirm the occurrence of the recently suggested high‐temperature phase transition in this crystal (at 133 °C). The corresponding transition in ND4D2PO4 observed here for the first time takes place at 141.5 °C. The mechanism involved in these transitions and those associated with the electrical conduction and dielectric anomalies are explained on the basis of the motional effects of the ammonium ions in these crystals. Conductivity values for deuterated crystals give direct evidence for the predominance of protonic conduction throughout the entire range of temperatures studied (30–260 °C). |
| URI: | http://dyuthi.cusat.ac.in/purl/2497 |
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| Dyuthi-P0282.pdf | (356.4Kb) |
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