scholarly journals Phase Diagram and Dielectric Relaxation Studies of n-Hexyl-isothiocyanato-biphenyl (6BT) in the Smectic E Phase under High Pressure

2002 ◽  
Vol 57 (5) ◽  
pp. 233-236 ◽  
Author(s):  
Stanislaw Urban ◽  
Albert Würflinger
Keyword(s):  
Phase Diagram ◽  
Dielectric Relaxation ◽  
Liquid Crystalline ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Temperature Phase ◽  
Short Axis ◽  
Frequency Range ◽  
Relaxation Measurements ◽  
Analogous Data

The pressure-temperature phase diagram of n-hexyl-isothiocyanato-biphenyl (6BT) at up to 190 MPa and 250 - 400 K was established with the aid of DTA. The dielectric relaxation measurements in the SmE phase of 6BT were performed in the pressure range of 0.1 - 150 MPa and the temperature range of 320 - 350 K. The Debye-type relaxation process was observed in the frequency range of 100 Hz - 100 kHz. The longitudinal relaxation time characterizing the molecular reorientations around the short axis was analyzed with respect to the pressure and temperature dependencies, yielding the activation volume, Δ#V = RΤ(∂ ln τ/∂p)Τ , and activation enthalpy, Δ#H = R(∂ ln τ/∂Τ-1)p , respectively. The results are compared with the analogous data obtained recently for 8BT and other similar compounds having the nematic and SmA liquid crystalline phases.in the telluride retain their molecular character, with small intercluster interactions.

The electrical conductivity of dry polycrystalline olivine compacts at high temperatures and pressures

2010 ◽  
Vol 74 (5) ◽  
pp. 849-857 ◽  
Author(s):  
Lidong Dai ◽  
Heping Li ◽  
Chunhai Li ◽  
Haiying Hu ◽  
Shuangming Shan
Keyword(s):  
Electrical Conductivity ◽  
Oxygen Fugacity ◽  
Conduction Mechanism ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Small Polaron ◽  
Frequency Range ◽  
Exponential Factor ◽  
Exponential Factors ◽  
The Relationship

AbstractThe electrical conductivity of dry polycrystalline olivine compacts (hot-pressed and sintered pellets) was measured at pressures of 1.0–4.0 GPa, at temperatures of 1073–1423 K, and at different oxygen fugacities via the use of a YJ-3000t multi-anvil press. Oxygen fugacity was controlled successfully by means of five solid buffers: Fe3O4-Fe2O3, Ni-NiO, Fe-Fe3O4, Fe-FeO and Mo-MoO2. Within the selected frequency range of 102–106 Hz, the experimental results indicate that the grain interior conduction mechanism is characterized by a semi-circular curve on an impedance diagram. As a function of increasing pressure, the electrical conductivity of polycrystalline olivine compacts decreases, whereas the activation enthalpy and the temperature-independent pre-exponential factors increase slightly. The activation energy and activation volume of polycrystalline olivine compacts were determined to be 141.02±2.53 kJ/mol and 0.25±0.05 cm3/mol, respectively. At a pressure of 4.0 GPa, electrical conductivity was observed to increase as a function of increasing oxygen fugacity, and the relationship between electrical conductivity and oxygen fugacity can be described as log10 (σ) = (2.47±0.085) + (0.096±0.023)×log10fO2 + (–0.55±0.011)/T, which presents the exponential factor q (˜0.096). Our observations demonstrate that the primary conduction mechanism for polycrystalline olivine compacts is a small polaron.

scholarly journals Influence of High Conductive Magnetite Impurity on the Electrical Conductivity of Dry Olivine Aggregates at High Temperature and High Pressure

Minerals ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 44 ◽  
Author(s):  
Lidong Dai ◽  
Haiying Hu ◽  
Wenqing Sun ◽  
Heping Li ◽  
Changcai Liu ◽  
...  
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
High Pressure ◽  
Percolation Threshold ◽  
Atmospheric Pressure ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Frequency Range ◽  
Arrhenius Relation ◽  
Conductivity Anomalies

The electrical conductivity of dry sintered olivine aggregates with various contents of magnetite (0, 3, 5, 7, 10, 20, and 100 vol. %) was measured at temperatures of 873–1273 K and a pressure of 2.0 GPa within a frequency range of 0.1–106 Hz. The changes of the electrical conductivity of the samples with temperature followed an Arrhenius relation. The electrical conductivity of the sintered olivine aggregates increased as the magnetite-bearing content increased, and the activation enthalpy decreased, accordingly. When the content of interconnected magnetite was higher than the percolation threshold (~5 vol. %), the electrical conductivity of the samples was markedly enhanced. As the pressure increased from 1.0 to 3.0 GPa, the electrical conductivity of the magnetite-free olivine aggregates decreased, whereas the electrical conductivity of the 5 vol. % magnetite-bearing sample increased. Furthermore, the activation energy and activation volume of the 5 vol. % magnetite-bearing sintered olivine aggregates at atmospheric pressure were calculated to be 0.16 ± 0.04 eV and −1.50 ± 0.04 cm3/mole respectively. Due to the high value of percolation threshold (~5 vol. %) in the magnetite impurity sample, our present results suggest that regional high conductivity anomalies in the deep Earth’s interior cannot be explained by the presence of the interconnected magnetite-bearing olivine aggregates.

Dielectric Studies on Liquid Crystals under High Pressure: VI. Low Frequency Relaxation Process in the Nematic and Smectic A Phase of 4-n-Octyl-4'-Cyanobiphenyl (8 CB)

1994 ◽  
Vol 49 (4-5) ◽  
pp. 552-558 ◽  
Author(s):  
S. Urban ◽  
T. Brückert ◽  
A. Würflinger
Keyword(s):  
Nematic Phase ◽  
Liquid Crystalline ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Low Frequency ◽  
Smectic A ◽  
Liquid Crystalline Phases ◽  
Smectic A Phase ◽  
Frequency Relaxation ◽  
Increasing Temperature

Abstract Dielectric relaxation studies of 4-n-octyl-4'-cyanobiphenyl (8 CB) were performed in the pressure range 0.1 -120 MPa, the frequency range 1 kHz -13 MHz and the temperature range 295-331 K. The dielectric behaviour of 8C B in the nematic phase is similar to that of 5 CB, 6 CB and 7 CB. In particular, the activation enthalpy decreases with increasing pressure and the activation volume decreases with increasing temperature in the nematic phase. In the smectic A phase of 8 CB both these parameters are markedly lower and show opposite pressure and temperature dependencies. We tentatively interpret these effects as a result of breaking of the dipole-dipole correlations which manifests itself differently in these liquid crystalline phases.

scholarly journals Static and Dynamic Dielectric Properties of Mesogenic n-Nonyloxycyanobiphenyl (9OCB)

2007 ◽  
Vol 62 (1-2) ◽  
pp. 61-66
Author(s):  
Grzegorz Czechowski ◽  
Jan Jadżyn
Keyword(s):  
Activation Energy ◽  
Phase Transitions ◽  
Dielectric Properties ◽  
Dielectric Relaxation ◽  
Rotational Diffusion ◽  
Short Axis ◽  
Frequency Range ◽  
Static Permittivity ◽  
Anomalous Temperature ◽  
Smectic A

The dielectric properties of n-nonyloxycyanobiphenyl in the isotropic (I), nematic (N) and smectic A (SA) phases were investigated. The dielectric relaxation spectra, recorded in the frequency range 50 kHz - 100 MHz, were analyzed with use of the Cole-Cole equation. An anomalous temperature behavior of the static permittivity, the rotational diffusion exponent and the activation energy of mesogenic molecules rotating around their short axis, observed in the vicinity of the phase transitions, are discussed.

Differential Thermal Analysis (DTA) and Dielectric Studies of 4 -(trans-4-Heptyl-Cyclohexyl)-benzonitrile (7PCH) under High Pressure

1995 ◽  
Vol 50 (11) ◽  
pp. 977-983 ◽  
Author(s):  
T. Brückert ◽  
D. Büsing ◽  
A. Würflinger
Keyword(s):  
Nematic Phase ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Retardation Factor ◽  
Isotropic Phase ◽  
Dielectric Studies ◽  
Frequency Range ◽  
Nmr Studies ◽  
Using Data ◽  
Increasing Temperature

Abstract With the aid of DTA the phase diagram of 4-(trans-4-heptyl-cyclohexyl)-benzonitrile, 7PCH, was redetermined. Dielectric studies on the static and complex permittivity have been performed on 7PCH in the pressure range 0.1 -220 MPa, the frequency range 1 kHz-13 MHz and the temperature range 290-380 K. For the slow relaxation process in the nematic phase, characterized by the relaxa­tion time tII , we have calculated the activation volume, Δ ≠VII, of about 80 to 60 cm3/mol (decreasing with increasing temperature), and the activation enthalpy, Δ ≠HII, of approximately 70 kJ/mol. The isochoric activation energy, Δ ≠UII, amounts to about 36 kJ/mol. The pressure dependence of Δ ≠HII is less pronounced compared with previous findings for 5PCH and 7CB. Estimates of t0 (extrapo­lated from the relaxation time in the isotropic phase) allow the calculation of the retardation factor gII = tII/t0 that is analysed in terms of theories of Martin-Meier-Saupe and Coffey in order to evalu­ate the nematic potential q. Using data for the order parameter 5 from NMR studies it was possible to determine the strength of the interaction potential in the nematic phase and to check the relation q~S which is valid at p = const., but not at V = const. The results are compared with recent findings for other homologous series.

Phase Diagram of the Ferroelectric Perovskite (Na0.5Bi0.5)1−xBaxTiO3 by Anelastic and Dielectric Relaxation Measurements

2012 ◽  
Vol 184 ◽  
pp. 339-344 ◽  
Author(s):  
Francesco Trequattrini ◽  
Francesco Cordero ◽  
Floriana Craciun ◽  
Elisa Mercadelli ◽  
Carmen Galassi
Keyword(s):  
Phase Diagram ◽  
Dielectric Relaxation ◽  
Phase Boundary ◽  
Monoclinic Phase ◽  
Structural Disorder ◽  
Extensive Study ◽  
Elastic Compliance ◽  
Relaxation Measurements ◽  
Ferroelectric Perovskite

Anelastic and dielectric relaxation measurements have been carried out on poled and unpoled samples of the ferroelectric perovskite (Na0.5Bi0.5)1−xBaxTiO3(NBT-xBT), with composition in the range between pure NBT and the morphotropic phase boundary, 0 ≤x≤ 0.08. The complex elastic compliance spectra contain clear indications of both the rhombohedral/tetragonal and tetragonal/cubic transitions, allowing the determination of the phase diagram, which is difficult to obtain by diffraction techniques due to the very low distortions in both the tetragonal and rhombohedral phases and to the structural disorder in the Na/Bi sublattice. An extensive study is made for concentrations in the region of the morphotropic boundary (x∼ 0.06) in order to find possible signatures of monoclinic phase, as for the case of PbZr1-xTixO3(PZT). The main features in the anelastic curves are compared with those in the dielectric spectra and are tentatively related to different modes of octahedral rotations and polar cation shifts.

Electrical conductivity studies on silica phases and the effects of phase transformation

2019 ◽  
Vol 104 (12) ◽  
pp. 1800-1805
Author(s):  
George M. Amulele ◽  
Anthony W. Lanati ◽  
Simon M. Clark
Keyword(s):  
Electrical Conductivity ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Hydrogen Charge ◽  
Charge Compensation ◽  
Composition Analysis ◽  
Conductivity Measurements ◽  
Pressure System ◽  
Electrical Conductivities ◽  
Silica Phases

Abstract Starting with the same sample, the electrical conductivities of quartz and coesite have been measured at pressures of 1, 6, and 8.7 GPa, respectively, over a temperature range of 373–1273 K in a multi-anvil high-pressure system. Results indicate that the electrical conductivity in quartz increases with pressure as well as when the phase change from quartz to coesite occurs, while the activation enthalpy decreases with increasing pressure. Activation enthalpies of 0.89, 0.56, and 0.46 eV, were determined at 1, 6, and 8.7 GPa, respectively, giving an activation volume of –0.052 ± 0.006 cm3/mol. FTIR and composition analysis indicate that the electrical conductivities in silica polymorphs is controlled by substitution of silicon by aluminum with hydrogen charge compensation. Comparing with electrical conductivity measurements in stishovite, reported by Yoshino et al. (2014), our results fall within the aluminum and water content extremes measured in stishovite at 12 GPa. The resulting electrical conductivity model is mapped over the magnetotelluric profile obtained through the tectonically stable Northern Australian Craton. Given their relative abundances, these results imply potentially high electrical conductivities in the crust and mantle from contributions of silica polymorphs. The main results of this paper are as follows:The electrical conductivity of silica polymorphs is determined by impedance spectroscopy up to 8.7 GPa.The activation enthalpy decreases with increasing pressure indicating a negative activation volume across the silica polymorphs.The electrical conductivity results are consistent with measurements observed in stishovite at 12 GPa.

scholarly journals Field-temperature phase diagram of the enigmatic Nd2(Zr1−xTix)2O7 pyrochlore magnets

2021 ◽  
Vol 103 (21) ◽  
Author(s):  
M. Léger ◽  
E. Lhotel ◽  
E. Ressouche ◽  
K. Beauvois ◽  
F. Damay ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Temperature Phase ◽  
Field Temperature ◽  
Temperature Phase Diagram
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