O. Tari

Calculation of the Raman frequencies as a function of pressure in the solid phases II and III (III’) of benzene

We calculate here the Raman frequencies of the lattice modes A(Ag), B(B2g) and C(B1gB3g) as a function of pressure at room temperature for the solid phases (II, III and III’) of benzene. This calculation is performed using volume data through the mode Grüneisen parameter. It is found that our calculated frequencies of those lattice modes increase with increasing pressure, as expected. Calculated frequencies are in good agreement with the measurements of the three lattice modes for the solid phases studied in benzene.

Molar volume calculated at various pressures and the Pippard relations close to the melting point in benzene

ABSTRACT The molar volume of solid and liquid benzene was calculated at various pressures (at constant temperatures), and the Pippard relations were examined close to the melting point in this organic molecule. The molar volume calculated is in good agreement with the observed data, which decreases as the pressure increases up to about 150 MPa. The Pippard relations are also valid within this pressure range at constant temperatures studied here for the solid and liquid phases of benzene.

Calculation of the CP-CV as a function of temperature close to the melting point in benzene

ABSTRACT The temperature dependence of the is calculated at constant pressures using the observed volume data from the literature for solid and liquid benzene near the melting point. Our calculated values are compared with some earlier treatments and we find that they disagree at constant pressures for the solid benzene, whereas for the liquid benzene agreement is reasonable in terms of the order of magnitude between our calculated and those predicted from the Peng–Robinson equation of state. Our calculated also agrees with the experimental data at normal pressure and has lower values at higher pressures in liquid benzene. Our treatment given here indicates that the and the heat capacity can be calculated from the molar volume as a function of temperature at constant pressures using the thermodynamic relations for the solid and liquid benzene near the melting point.

Temperature effect on the structural ferroelectric – paraelectric transition in Li2Ge7O15

abstract Li2Ge7O15 (LGO) undergoes the ferroelectric – paraelectric transition at Tc =283.5K. The crystal structure of LGO is orthorhombic with the four formula units in the unit cell in the paraelectric phase (T < TC) . The ferroelectric phase of LGO (T < TC) has also the orthorhombic crystal structure with the pseudotrigonal symmetry of the unit group. In this study, we investigate the structural ferroelectric – paraelectric phase transition in Li2Ge7O15. Temperature effect on various physical properties such as the dielectric constant, spontaneous polarization, reflected intensity related to the order parameter, the Raman frequencies of the lattice (Ag) modes and the linear thermal expansion, is studied here by analyzing the experimental data from the literature close to the ferroelectric - paraelectric transition in Li2Ge7O15. An order-disorder type of transition is indicated on the basis of our analyses of the physical properties studied here within the mean field (molecular field) theory for the ferroelectric - paraelectric transition in Li2Ge7O15.

Variation of the Raman frequency of a soft mode with the pressure (20 oC) for the phase transitions in NH4F

The Raman frequency of a soft mode (238 cm -1 ) is analyzed as a function of pressure at 20 o C for NH 4 F using the experimental data from the literature. This analysis is performed for the pressure dependence of the Raman frequency shifts (1 / n )( ¶ n / ¶ P) T of the soft mode close to the I - III, III - V and V – VI transitions in NH 4 F. The frequency shifts increase as the pressure increases toward the phase transitions at T = 20 o C (293 K) in this ammonium structure. From the frequency shifts of the soft mode studied, the pressure dependence of the isothermal compressibility is predicted through the mode Gruneisen parameter. Our calculated isothermal compressibility can be compared with the experimental measurements.

Pippard relation close to the alpha – beta transition for quartz in granite

In this study, we examine variation of the thermal expansion αp with the isothermal compressibility κT at various temperatures (1 atm) close to the α-β transition in quartz using the experimental data from the literature. We obtain the pressure dependence of the thermal expansion for dry granite quartz at room temperature. Variation of αp with the κT is also studied as a function of temperature for constant pressures of 0.1, 100, 200 and 300 MPa close to the α-β transition of dry granite quartz. Our results show that volumetric expansion increases as functions of temperature (1 atm) and pressure (room temperature), as observed experimentally for dry granite quartz.

Analysis of the thermal expansivity near the tricritical point in dilute chromium alloys

Chromium (Cr) undergoes a first order Neel transition as an antiferromagnetic material. When V, Mo and Mn atoms are substituted in the Cr lattice, a weak first order Neel transition in pure Cr changes toward a second order transition and a possible tricritical point in CrV occurs close to 0.2 at %V, as observed experimentally from the measurements of the thermal expansivity at various temperatures. In this study, we analyze the experimental data for the thermal expansivity from the literature as a function of temperature using the power - law formula for Cr alloys (Cr - 0.1V, 0.2V, 0.5V and Cr - 0.1Mn, Cr - 0.2Mo, 0.3Mo, 0.4Mo). Our results are interpreted near the tricritical point in dilute chromium alloys.