Pressure Dependence Of Transition Temperature Research Articles

The effect of hydrostatic pressure up to 1.61 GPa on the Morin transition of hematite‐bearing rocks: Implications for planetary crustal magnetization

AbstractWe present new experimental data on the dependence of the Morin transition temperature (TM) on hydrostatic pressure up to 1.61 GPa, obtained on a well‐characterized multidomain hematite‐bearing sample from a banded iron formation. We used a nonmagnetic high‐pressure cell for pressure application and a Superconducting Quantum Interference Device magnetometer to measure the isothermal remanent magnetization (IRM) under pressure on warming from 243 K to room temperature (T0). IRM imparted at T0 under pressure in 270 mT magnetic field (IRM270mT) is not recovered after a cooling‐warming cycle. Memory effect under pressure was quantified as IRM recovery decrease of 10%/GPa. TM, determined on warming, reaches T0 under hydrostatic pressure 1.38–1.61 GPa. The pressure dependence of TM up to 1.61 GPa is positive and essentially linear with a slope dTM/dP = (25 ± 2) K/GPa. This estimate is more precise than previous ones and allows quantifying the effect of a pressure wave on the upper crust magnetization, with special emphasis on Mars.

Collapse of CuO Double Chains and Suppression of Superconductivity in High-Pressure Phase of YBa2Cu4O8

The crystal structure and electrical resistivity of YBa2Cu4O8 (Y124) were studied under high pressure up to 18 GPa using diamond-anvil cells, respectively, in order to clarify its conduction mechanism. Y124 causes the first-order phase-transition into the orthorhombic Immm at pressure around 11 GPa. The high-pressure phase (HPP) also shows the superconductivity, while the manner of temperature dependence of electrical resistance and the pressure dependence of transition temperature, Tc, drastically change above 11 GPa. The CuO2 plane persists in HPP but the CuO double chains collapse with the phase transition and transform into three-dimensional Cu–O network, resulting in the renewal of conduction system.

Phase transition studies in symmetric dimeric liquid crystals

As a part of the systematic studies on symmetric liquid crystal dimer homologous series, α,ω-bis-(4-n-alkylaniline benzylidene-4′-oxy) alkanes, (referred to as m.OnO.m with m = 3, 4, and 5; and n = 8, 9, and 10), we present in this article the nature of phase transitions across isotropic–nematic and nematic–smectic-A (N–SmA) phases exhibited by the just mentioned compounds. The methods employed are differential scanning calorimetry and dilatometry. The compounds studied were 3.O8O.3, 4.O8O.4, and 5.O8O.5; and 3.O9.03, 5.O9O.5, 3.O10O.3, 4.O10O.4, and 5.O10O.5. Different from the case of their corresponding monomers, all these compounds exhibit a nematic phase only with the exception of 5.O8O.5 which exhibits a SA phase in addition to the nematic phase. The phase transitions viz., isotropic–nematic transitions studied in all these compounds were confirmed to be of first-order nature, whereas the N–SmA transition exhibited by the compound 5.O8O.5 only was found to be of second-order nature. We also report in this article the calculated density jumps, thermal expansion coefficient maxima, and pressure dependence of transition temperatures which are analyzed in the light of the available literature data.

Phase Transition Studies of 6.O12O.6 and 7.O6O.7 Using Density Measurements

The symmetric liquid crystal dimer homologous series, α,ω-bis-(4-n-alkylaniline benzylidene-4′-oxy) alkanes, show a rich variety of smectic polymorphism. We report here the nature of different transitions exhibited by two of these dimers using density measurements as a function of temperature. The compound 6.O12O.6 exhibits only nematic phase; while 7.O6O.7 exhibits smectic A and smectic F phases. All the phase transitions studied viz., isotropic – nematic, isotropic – smectic A, and smectic A – smectic F are confirmed to be of first order nature. The calculated density jumps, thermal expansion coefficient data and pressure dependence of transition temperatures are analysed in the light of available literature data.

Phase transition studies in mesogenic dimers

AbstractSchiff base liquid crystal dimers, both symmetric and non‐symmetric, in which two anisotropic groups are linked by a flexible spacer, exhibit a rich variety of smectic mesomorphism. The interest in this class of mesogens stems not only from their ability to act as model compounds for semi‐flexible mainchain liquid crystal polymers but also from their quite different properties compared to conventional low molar mass liquid crystals (monomers). We report here the phase transition studies on two examples of these schiff base liquid crystal dimers using the Differential Scanning Calorimetry and density measurements as a function of temperature. The symmetric liquid crystal dimer, α,ω‐bis (4‐n‐dodecylaniline benzylidene‐4′‐oxy)decane (10.O12O.10) exhibits a very rare Isotropic to G transition. Where as, the non‐symmetric dimer, α‐(4‐cyano biphenyl‐4′‐yloxy)‐ω‐(4‐n‐decylanilinebenzylidene‐4′‐oxy)decane (CB.O10O.10) exhibits a rare nematic to intercalated smectic A phase transition. The transitions studied, isotropic to nematic and isotropic to G exhibit a large density jump at the transition confirming their first order nature. Nematic to intercalated smectic A transition is found to be a second order transition whose behavior is similar to nematic to smectic A transition. Calculated values of pressure dependence of transition temperature and thermal expansion coefficient are also reported.

INVESTIGATION OF RARE PHASE TRANSITIONS BY DENSITY MEASUREMENTS

We report here the study of nature of few rare phase transitions viz., Isotropic ‒ Sm C, Sm C ‒ Sm F and Srn A ‒ Sm F transition in two homologues of α, ω-bis(4-n-alkylanilinebenzylid- ine-4′-oxy)alkane series using density measurements. Compound 10.040.10 exhibits Iso- tropic ‒ Sm C, Sm C ‒ Sm F and Sm F ‒ Crystal phase transitions. Whereas 10.0100.10 exhibits Isotropic ‒ Sm A, Sm A ‒ Sm F and Sm F ‒ Crystal transitions. Variation of density with temperature across the phase transitions Isotropic ‒ Sm A, Isotropic ‒ Sm C, Sm C ‒ Sm F and Sm A ‒ Sm F show a jump in density confirming that all these transitions are first order in nature. However, the magnitude of the density jump is smaller than expected at some of these transitions. The calculated pressure dependence of transition temperature is also reported.

Density Studies on Two Homologues of α,ω-Bis(4-n-Alkylanilinebenzylidine-4′-Oxy) Alkanes

α,ω-bis(4-n-alkylanilinebenzylidine-4′-oxy)alkanes exhibit a rich smectic polymorphism. We have studied the variation of density as a function of temperature across the phase transitions in two compounds of the series viz., 7.O4O.7 and 7.O5O.7. Both of these compounds exhibit a rare phase transition of Sm A - Sm F. The results confirmed first order nature of the transitions of Isotropic - Sm A and Sm A - Sm F, but with a smaller jump than expected in density as compared to monomers across the transitions. The estimated pressure dependence of transition temperature is also reported. The results are discussed in the light of available literature data.

Pressure dependence of the superconducting state parameters of metallic glass superconductor Mg70Zn30

Explicit expressions have been derived for the volume dependence of electron-phonon coupling strength (λ) and the Coulomb pseudopotential (μ*) considering the variation of Fermi momentum (κF) and Debye temperature (θD) with volume. Ashcroft’s model pseudopotential and RPA form of dielectric screening have been used for obtaining pressure dependence of transition temperature (TC) and the logarithmic volume derivative (Φ) of the effective interaction strength (N0V) for metallic glass superconductor Mg70Zn30. It has been observed that TC of the metallic glass Mg70Zn30 decreases rapidly with increase of pressure and the superconducting phase disappears at about 30% decrease of volume, for which the μ* curve shows a minimum and an elbow is formed in the Φ graph.

Growth of Smectic B (Crystal) and Phase Transitions in Liquid‐Crystalline PBnA (n = 4, 5, and 6) Compounds

AbstractThermal microscopy, calorimetric (DSC) and dilatometric investigations are reported in three liquid‐crystalline compounds of n(4‐n‐phenylylbenzylidene) 4‐n‐alkylaniline series viz., PBnA for n = 4, 5, and 6. They exhibit nematic, smectic B (cryst) and smectic E (monotropic) polymorphism. Effective role of terminal phenyl end chain is discusscd for the occurrence of 3D‐ordered smectic B and smectic E phases. Density jumps and associated volume expansion coefficient anomaly infer first order nature of isotropic to nematic (IN) and nematic to smectic B (NB) transitions. Exponental growth of three‐dimensional hexagonal positional correlations estimated in the vicinity of nematic to smectic B transition through the β exponent infers the Van der Waals type of molecular interactions. Pressure dependence of transition temperatures are estimated, IN and NB transitions and thermal stablity are discussed.

Density studies in terephthalylidene-bis-p-n-alkylanilines

Abstract The temperature dependence of density in terephthalylidene-bis-p-n-alkylanilines (TBAA5 and 6) is studied to investigate the phase transitions, associated volume jumps, order of the transitions, estimated pressure dependence of transition temperatures, and pretransitional effects. The compounds exhibit nematic, smectic A, smectic C, smectic F, smectic G and smectic H phases with higher clearing temperatures. The smectic A to smectic C transition, which is a fluctuation induced first order transition in TBAA5, is found to be a second order transition in TBAA5 and 6. The results are discussed in the light of other experimental reports. The estimated pressure dependence of transition temperatures along with the reported experimental P[sbnd]T data are discussed. The N[sbnd]SA transition is first order in TBAA5 and 6. The studies across other transitions are also discussed.

Phase transitions in ferro-electric liquid crystal dobambc by density

Thermal microscopy, differential scanning calorimetry and dilatometric investigations are carried out on the ferroelectric liquid crystal N(p-n-Decyloxybenzylidene) p-amino 2-methylbutyl cinnamate viz., DOBAMBC which exhibits smectic-A, smectic-C* and monotropic Smectic-H phases. The isotropic-smectic-A (IA), smectic-A-Smectic-C* (AC*) and smectic-C*-Smectic-H (C*H) transitions are found to be first order. Detailed study of pre-transitional effects inferred the nucleation growth analogy to IA transition and a clear first order AC* transition in contrast to predicted second order AC transition. The estimated pressure dependence of transition temperatures using the molar volume and enthalpy data are presented.

Pressure dependence of transition temperature in selected high-Tc superconductors

Abstract In this paper we report recent determinations of Tc(p) from the complex ac-susceptibility for both single- and polycrystalline Tl2Ca1Ba2Cu2O8 and Y1Ba2Cu3O7 using a helium gas system to 10 kbar and a hydrostatic metal—gasket cell to 35 kbar.

Density studies across smectic‐smectic transitions in 70.6 and 80.10

AbstractThe temperature dependence of density in N(p‐n‐heptyloxy benzylidene) p‐n‐hexylaniline (70.6) and in N(p‐n‐octyloxy benezylidene) p‐n‐decylaniline (80.10) is carried out to study the nature of the phase transitions associated density jumps, to estimate the pressure dependence of transition temperatures and pretransitional effects. The compounds 70.6 exhibits a phase variant ACFG whereas 80.10 exhibits a new phase sequence variant ABF. The isotropic‐smectic A, semctic A‐smectic B and semctic C‐smectic F phase transitions are found to be first order. The calculated thermal expansion coefficient also supported the density results. The density jumps, associated enthalpies and estimated pressure dependence of transition temperatures at the isotropic‐smectic A phase transformation in other compounds are presented.

Density and ultrasonic velocity studies inN(p-n-heptyloxybenzylidene)p-n-pentylaniline

Abstract The density and ultrasonic velocity of N(p-n-heptyloxybenzylidene) p-n-pentylaniline (70.5) are measured as a function of temperature from the isotropic liquid to the smectic B phase. The compound is pentamorphic, exhibiting four smectic phases, viz. smectic G, smectic B, smectic C, smectic A, and a nematic phase. The changes in density, ultrasonic velocity and the derived parameters confirm the N-I and SB-SC transitions as first-order, the SA-N transition as weak first-order, and SC-SA transition as second-order. An estimate of the pressure dependence of transition temperatures is presented. The computed parameters: adiabatic compressibility β ad , molar sound velocity Rn and molar compressibility Aw , are discussed.

Physical Properties Related to Phase Transitions in Na2CO3 Crystals

Several physical properties related to phase transitions in Na 2 CO 3 crystal were experimentally studied. Ferroelasticity was confirmed above 200°C. The temperature dependence of birefringence was measured. Pressure dependence of transition temperatures were studied above room temperature. In addition, specific heat and electric capacity in low temperature region were measured, but no distinct anomalies associated with the reported lock-in transition could be found.

The pressure dependence of the transition temperature in KDP and ADP

The pressure dependence of the ferroelectric transition temperature for KD 2PO 4 and for K(D 0.55H 0.45) 2PO 4 has been measured to 10 kbar. The dependence in both cases was linear, with slopes of -2.40 ± 0.01 °K/kbar and −2.93±0.01 °K/kbar respectively. Measurements on ND 4D 2PO 4 and NH 4H 2PO 4 over a smaller pressure range gave linear fits with slopes of -1.43 ± 0.04 °K/kbar and -3.39 ± 0.06 °K/kbar respectively. The results were obtained by neutron diffraction wherein the transition was detected by the sharp decrease of extinction effects on transforming to the low temperature phase. The present results on KDP are consistent with previous neutron diffraction measurements utilizing samples with 0 per cent and approx. 90 per cent deuteration. The values for dT c/dP are found to be approximately 1 °K/kbar less negative than those determined from dielectric constant measurements.

Transitions and Phases of Polytetrafluoroethylene

Behavior of transitions and the nature of high-pressure phase in polytetrafluoro ethylene are studied using methods of ultrasonic waves, thermal expansion, differential thermal analysis and X-ray diffraction. A phase diagram is obtained in pressure range from 1 atm. to 6,500 kg/cm2 and in temperature range from room temperature to 165°C. Three phases are found; phase I above 30°C, phase II below 20°C, both at 1 atm. and phase III above 5,000 kg/cm2. The triple point is located at 75°C and 5,000 kg/cm2. Pressure dependence of transition temperatures is obtained as 15 and 9 degrees per 1,000 kg/cm2 for the 20°C and 30°C transitions at low pressure, 9 degrees per 1,000 kg/cm2 for both transitions at intermediate pressure range from about 3,000 to 5,000 kg/cm2, -13 and 50 degrees per 1,000 kg/cm2 for the II–III and the III–I transitions, respectively. It is suggested that the high-pressure phase (phase III) may be a closely packed but disordered phase.

Theory of -Transition in Solid Hydrogen

A theory of A-transition in solid hydrogen is developed on the basis of quadrupole-quadrupole interaction between ortho-hydrogen molecules. The double time Green's function technique is adopted to investigate the ground state configuration, low lying excitations and the tempera­ ture dependence of long range order in a self-consistent way. The inelastic scattering cross section of neutron by solid hydrogen due to the excitation of libration waves is also calculated. It has been known that normal hydrogen undergoes a phase transitiOn ac­ companied by a J.-shaped anomaly in specific heat at about 1.5° K. This transition is believed to be related closely to the removal of the three-fold degeneracy in rotational states of ortho-molecules and many experimental evidences to support this supposition have been accumulated. The observations of the specific heat anomaly, l) of a line shape change in nuclear magnetic resonance 2 ) and of the dependence of transition temperature on ortho-molecule concentrations 3 ) are such examples. Furthermore the fact that the interaction responsible for the removal of the degeneracy mentioned above mainly comes from the quadrupole-quadrupole interaction between ortho-molecules has been proved by the theoretical analysis of the anomalous specific heae) and by the experiment on pressure dependence of transition temperature. 5 ) Theoretical investigations of this phase transition are already abundant. Among them, Tomita 6 ) laid emphasis on the cooperative nature in the transition and tried a theory of order-disorder transition with the Weiss and Bethe ap­ proximations. At that time, however, the molecular interaCtion responsible for the transition was not yet clear, and hence microscopic theories of the ordered phase and of phase transition which take account of the correct interactions have appeared comparatively recently. Many attempts have been made to find the ordered orientation of molecules in solid ortho-hydrogen with the lowest energy. Nagai and Nakamura 7 ) have obtained the lowest energy state of the quadupole moment array in fcc lattice by generalizing Luttinger and Tisza's method. 8 ) On the other hand, for the hcp structure Danielian, 9 ) Kitaigorodskii and Mirskaya/ 0 ) and Felsteiner 11 ) have proposed different orderd configurations of ortho-hydrogen molecules with the lowest classical quadrupole energy. All these authors have ignored the quantum effect which is not necessarily small

The pressure dependence of transition temperature in some superconductors

The pressure dependence of transition temperature in some superconductors