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Chapter V Dielectric Study of …… - glutamic acid, L-histidine and L-valine) doped KDP crystals was carried out by Kumaresan and Kumaresan [46, 47]. The authors found that on doping of amino acids the value of dielectric constant of KDP crystals decreased and also decreased with increase in the frequency of applied field. Moreover, L- arginine, L-histidine and glycine doped KDP crystals were grown by Kumar and Babu [48]. They have studied the dielectric behavior and found the dielectric constant and dielectric loss less in doped crystals in compare to pure KDP crystals. Udupa et al [49] have found for KDP crystals that the dielectric constant decreases with the increase of temperature at all frequencies studied. The same authors also have observed the appreciable increase in the value of dielectric constant after impurity (MgO) addition and decrease in its value with increase in frequency. An anomalous dielectric behavior in ferroelectric KDP was noticed by Gilchrist [50]. The dielectric permittivity ε = ε’ – ε” of KDP pressed powder was measured between temperature from 1.4 K to 25 K in the presence of d.c. electric field bias. Usually, if the bias was switched at time t = 0, the ε’ and ε” would jump to new values and then decrease approximately as log t (6 < t < 20000 S). This well-know effect, which is also found in single crystals, can be attributed to the switchable micro-domains present accidentally in crystals but present more in powders. A very different type of after effect was observed in a narrow temperature range from 7 K to 8 K. The ε’ jumped to lower value, thereafter increased with t according to a stretched exponential with a temperature dependent time constant. This is similar to the extrapolation of the Arrhenius law of known but unassigned weak-field 209
Chapter V Dielectric Study of …… - dispersion i.e. a property of poly-domain single crystals as well as powders. The weak field dispersion is due to the elementary movement of a jog on a lateral step displacement of a domain wall, consisting of a single H-bond reversal. This is anomalous effect results from the interaction between these point defects and the micro domain systems. Moreover, the high frequency dielectric measurements were carried on Lithium ion added KDP crystals in X-band region (8 to 12 GHz) of microwave frequencies at room temperature by Shirsat et al [51]. The authors selected three different lengths of crystals. Initially the standing wave pattern was obtained for with and without sample and the wavelength was determined and then the dielectric constant was calculated by using the suitable formula [52]. Also, in another study the dielectric constant values were obtained comparatively low for Li + ion added KDP crystals than the pure KDP crystals within the frequency range 8 GHz to 12 GHz. This suggested that the Li + ion added KDP crystals were more suitable for high speed electro-optic modulation than pure KDP crystals [53]. Similarly high frequency dielectric study of thiourea doped KDP crystals was carried out in X-band region of micro-wave frequency by Hussain et al [54]. They also found that the dielectric constant of thiourea doped KDP was less than the pure KDP crystals. In the present chapter, the dielectric properties of different amount of (0.3, 0.4 and 0.5 weight percentage) L-histidine, L-threonine and DL- methionine doped KDP crystals are reported. The single crystals of pure and amino acid doped KDP crystals were grown by the slow aqueous solution evaporation technique, which is described in Chapter-II. 210
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Saurashtra University Re - Accredit
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Statements Under O. Ph.D.7 of Saura
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ACKNOWLEDGEMENT The author expresse
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in-law, Mother- in -law and all oth
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of NLO materials in rapidly develop
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doped samples in comparison to the
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micro-hardness decreases. Also, as
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Papers Published in National and In
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Seminar on Recent Advances in Conde
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Chapter I Brief Introduction... Cha
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Chapter II Solution Growth…. Tabl
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Chapter VIII Micro-hardness studies
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Load (N) Chapter VIII Micro-hardnes
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Chapter IX General Conclusion case
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