Tris-sarcosine calcium chloride (TSCC) is a highly uniaxial ferroelectric with a Curie temperature of approximately 130K. By suppressing ferroelectricity with bromine substitution on the chlorine sites, pure single crystals were tuned through a ferroelectric quantum phase transition. The resulting quantum critical regime was investigated in detail -the first time for a uniaxial ferroelectric and for an organic ferroelectric -and was found to persist up to temperatures of at least 30K to 40K. The nature of long-range dipole interactions in uniaxial materials, which lead to non-analytical terms in the free-energy expansion in the polarization, predict a dielectric susceptibility varying as 1/T 3 close to the quantum critical point. Rather than this, we find that the dielectric susceptibility varies as 1/T 2 as expected and observed in better known multi-axial systems. We explain this result by identifying the ultra-weak nature of the dipoles in the TSCC family of crystals. Interestingly we observe a shallow minimum in the inverse dielectric function at low temperatures close to the quantum critical point in paraelectric samples that may be attributed to the coupling of quantum polarization and strain fields. Finally we present results of the heat capacity and electro-caloric effect and explain how the time dependence of the polarization in ferroelectrics and paraelectrics should be considered when making quantitative estimates of temperature changes induced by applied electric fields.There has been a great deal of interest recently in the field of ferroelectric quantum phase transitions [1,2]. A chief reason for this is that the properties of ferroelectrics may be readily tuned with gate voltages and strains, which make quantum ferroelectrics and paraelectrics particularly suited for applications in advanced cryogenic electronics. Highlighting SrTiO 3 as an example, one sees that a pristine optically transparent insulator with a band gap of more than 3eV, and a static dielectric constant greater than 10 4 , may be tuned through an insulator to metal to superconductor transition and back again with the application of just a few volts [3,4]. On the other hand modest strains [5], chemical doping [6] or isotope substitution [1,7], can induce ferroelectricity in an otherwise paraelectric ground state. Ferroelectric quantum critical fluctuations have been observed up to temperatures higher than those often seen in other systems, and over a wide range of tuning parameters. Proximity to a displacive ferroelectric quantum critical point where the transverse optical phonon frequency becomes very small, and the dielectric function can rise to very high values, is believed to be of importance in understanding superconductivity in materials such as chemically doped [8] or ionic-liquid-gated SrTiO 3 [7] and KTaO 3 [4], and in oxide interface materials [9] to name just a few.The nature of quantum criticality in ferroelectrics is strikingly different from that found in other systems, for example magnetic systems [1,10,11]. Quantu...

9 ] However, the ultra-weak nature of the dipole moment in TSCC referred to below may reduce the effects of such long-range dipole interactions to a narrow temperature region around the critical point. This would mean that more conventional classical or quantum critical behaviour would be expected over a wider range of temperatures and tuning parameters. TSCC is hydrogen bonded and was characterized in the past as order-disorder albeit with no direct supporting evidence. [ 16,17 ] Since the time of these studies TSCC has come to be a prototypical displacive ferroelectrics, [ 18 ] as demonstrated by the existence of an under-damped soft mode. This mode can be followed into the GHz frequency regime [ 19 ] from high-T values of ca 630 GHz = 21 cm −1 . Deuteration [ 20 ] produces little change in T C , implying that the transition is not controlled by the N-Cl-hydrogen bonds, a result compatible with the soft-mode mechanism operating in TSCC. [ 2 ] The Curie constant of pure TSCC is 27 K, the smallest known Curie constant of any known ferroelectric. By way of comparison, typical values for oxide perovskites such as BaTiO 3 are 50 000 K. This puts TSCC in the family of ultra-weak ferroelectrics. An unrelated form of weak ferroelectricity arises in certain multiferroics where small polarizations are induced by magneto-electric coupling. In pure TSCC, the Curie constants near T C = 130 K, taken as the inverse slopes of the inverse dielectric constants versus temperature above and below T C , differ by a factor of 2.0. This ratio is that predicted by the simplest mean-fi eld Landau theory of phase transitions, but in fact exists in almost no other known ferroelectric. The ratio between the slopes in other ferroelectrics is typically greater than two due to the coupling between lattice strain and polarization. [ 21 ] Under modest pressures pure TSCC becomes what has been termed antiferroelectric, [ 22 ] although no supporting X-ray or dielectric evidence has been given for that label. Four additional enigmatic anomalies have been detected at 42 K, 64 K, 185 K, and another at 283 K [ 3 ] at ambient pressures. The supposed phase transition found near 283 K was described as a modulated quasi-hexagonal phase. [ 23 ] Another possible phase transition was found near 185 K as observed in the relaxation time in proton nuclear magnetic resonance (NMR) spectroscopy. [ 24 ] An additional phase transition was found using specifi c heat at 64 K [ 25 ] and verifi ed by dielectric loss and ultrasonic spectroscopy measurements. [ 26 ] A fourth transition was found near 42 K in dielectric measurements, [ 27 ] and was later confi rmed by resonant ultrasonic spectroscopy (RUS) [ 19 ] and specifi c-heat measurements. At present these anomalies involve unknown changes in the structure.Some studies have reported the phase transition at 64 K (by either dielectric or specifi c-heat data), and some studies have Quantum phase transitions occur in the halide salts of trissarcosine. [ 1 ] Substitution of bromine or iodine for chlorine in (CH 3 NHCH...

This Article contains an error in the spelling of the author A. Yazdani, which is incorrectly given as A. Yadzani. The error has not been fixed in the original PDF and HTML versions of the Article.

Presence of water content or moisture promotes premature thermal aging which hampers the properties of inhibited, isoparaffinic transformer oil used in electric multiple unit (EMU) train. Unpurified aged oil with high water presence is collected from the traction transformer and contaminants is removed using Double-Stage Vacuum Insulation Oil Regeneration Filtration Machine to produce purified aged oil. New transformer oil is selected as a control sample. The objective of this study is to investigate the effect of oil purification process on the thermal conductivity and breakdown voltage of the oil samples. Thermal conductivity measurement was done from temperatures of 30°C to 70°C. Dielectric characteristics are shown by analyzing breakdown voltage. Unpurified oil shows an increment from 1.54% to 3.13% as compared to new oil in response to temperature variation whereas purified oil has the lowest thermal conductivity value. However, breakdown voltage of purified oil is higher than unpurified oil and slightly lower than new oil. From this, it can be inferred that presence of water gives positive impact towards thermal properties and vice versa to dielectric properties. A relationship between thermal conductivity, breakdown voltage and presence of water has been deduced at the end of the study.

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