Explore the vast range of titles available.

The lattice stability and phonon response of Ti 3 C 2 T x MXene at high pressure are important for understanding its mechanical and thermal properties fully. Here, we use in situ high hydrostatic pressure X-ray diffraction (XRD) and Raman spectroscopy to study the lattice deformation and phonon behavior of Ti 3 C 2 T x MXene. XRD spectra indicate that no phase transformation occurs up to the pressure of 26.7 GPa. The elastic constant along a lattice parameter was calculated to be 378 GPa. In the Raman spectra obtained at high-pressure, the out-of-plane phonon modes ( A 1g at ~ 210, ~ 504, and ~ 711 cm −1 ) exhibit monotonic blueshifts with increasing pressure. The Grüneisen parameters of these three modes were calculated to be 1.08, 1.16, and 0.29, respectively. These results enrich the basic property data of Ti 3 C 2 T x MXene and would benefit the further understanding of this novel material.

Clinohumite is a potentially abundant silicate mineral with high water concentration (2-3 wt% H2O) that is generated from dehydration of serpentine-group minerals in subduction zones. Previous studies show that fluorine substitution (OH-=F-) can stabilize clinohumite to significantly higher temperature in subduction zones, although temperatures within the slabs are thought to be well within the stability field of both F-bearing and OH-clinohumite. We collected in-situ high-temperature Raman and Fourier transform infrared (FTIR) spectra for both the synthetic [Mg9Si4O16(OH)2] and natural [Mg7.84Fe0.58Mn0.01Ti0.25(SiO4)4O0.5(OH)1.30F0.20] clinohumite samples up to 1243 K. Three OH bands above 3450 cm-1 are detected for both the natural and synthetic samples with negative temperature dependence, due to neighboring H-H repulsion in the crystal structure. Additional OH peaks are detected for the natural sample below 3450 cm-1 with positive temperature dependence, which could be explained by non-polar F- substitution in the OH site. Hence, F- substitution significantly changes the high-temperature behavior of hydrogen bonds in the humite-group minerals. On the other hand, we evaluated the mode Gruneisen parameters (γiP, γiT), as well as the intrinsic anharmonic parameters (αi) for clinohumite, chondrodite, and phase A, the dense hydrous magnesium silicate (DHMS) phases along the brucite-forsterite join. The estimated averaged anharmonic parameters (αi_avg) for these DHMS phases are systematically smaller than those of olivine. To model the thermodynamic properties of minerals (such as heat capacity) at the high-temperature conditions of the mantle, the DeBye model, which simply approximates the lattice vibrations as harmonic oscillators, is commonly used. In contrast to forsterite, such quasi-harmonic approximations are valid for clinohumite at subduction zone temperatures, as the anharmonic contribution is no more than 2% when extrapolated to 2000 K. Hence, the classic DeBye model can reasonably simulate the thermodynamic properties of these DHMS phases in subduction zones.

We have predicted melting temperatures of ionic and partially covalent compounds viz. NaCl, NaF, LiF, MgO, CaF 2 , SiC at high pressures. The volume dependence of Grüneisen parameter determined from the Jeanloz equation has been used in the Lindemann law to predict melting curves. The pressure–volume relationships used in computations are determined with the help of the Holzapfel equation of state based on the adapted polynomial expansion of second order. The results for melting curves of different solids obtained in the present study using γ ∞ = 1 / 2 at extreme compression are found to be in reasonably good agreement with the available experimental data. We have also calculated slopes of melting curves at different pressures for the six compounds under study. It is found that the melting slopes decrease continuously with the increase in pressure, and tend to zero in the limit of infinite pressure. The results obtained in the present study are found to compare well with the experimental data and molecular dynamics simulations.

In the present work we have perform a comparative study of structural and elastic properties of some inorganic and organic molecular crystals viz. Realgar As 4 S 4 , As 4 S 3 , C 14 H 10 (anthracene), C 10 H 8 (naphthalene). For theoretical prediction, four different EOSs have been used viz. modified Lenard-Jones EOS (M-L Jones EOS), Brennan-Stacey EOS, Hamma—Suito EOS and Thomsen EOS. Further, we have checked the applicability of these EOSs for calculation of Grüneisen parameter at different compressions. Experimental data and theoretical facts give the validity of our work.

High-pressure and high-temperature Raman spectroscopic measurements of synthetic liebenbergite and Ni 2 SiO 4 spinel have been conducted up to 22 GPa and 700 ℃, respectively. Isothermal and isobaric mode Grüneisen parameters were calculated based on the observed Raman modes. The intrinsic anharmonicities of liebenbergite and Ni 2 SiO 4 spinel were also evaluated. The changes of the asymmetric SiO 4 stretching band of Ni 2 SiO 4 spinel in frequency are irreversible under decompression, indicating a potential pressure-induced modification in the crystal structure at elevated pressures. The values of isothermal mode Grüneisen parameters show that the SiO 4 internal vibrations in Ni-rich olivines are more sensitive to the variations of pressure. For spinel-group minerals, the SiO 4 internal vibrations can be less sensitive to the pressure change due to nickel incorporation. In contrast, according to the values of isobaric mode Grüneisen parameters, nickel increases the sensitivity of these vibrations to the variations of temperature. In addition, nickel has distinctive effects on the intrinsic anharmonicities of different vibration modes in both olivine and spinel-group minerals, and therefore alter the thermodynamic properties of their crystal structures.

In the present study, the variation in melting temperature of alkali halides is studied with repect to pressure using the Lindemann –Gilvarry law for melting. The model requires the value of Grüneisen parameter along with volume compression. The Equation of state used to estimate the variation of volume with isothermal pressure is Goyal and Gupta EoS. The EoS satisfies Stacey’s criteria which confirm the validity of Goyal and Gupta EoS at high pressure values. It is found from model calculations that Grüneisen parameter decreases with increase in pressure, however, melting temperature increases with pressure non-linearly as the slope of melting curve is found to decrease continuously as pressure increases. The variation of Grüneisen parameter with pressure matches with the general trend of variation as depicted in previous studies. The present computed results for pressure dependent melting temperature are compared with the available experimental results which present a good consistency between the compared results. The approach formulated can be used to estimate the melting temperature of solids at high pressure values and is simpler than DFT computations.

In situ high-temperature Raman and Fourier transform infrared spectra were measured for aragonite, strontianite, cerussite, and witherite at ambient pressure. The orthorhombic to trigonal phase transitions were observed by the vibrational spectra for aragonite and witherite, at the temperatures of 773 and 1150 K, respectively. The isobaric mode Grüneisen parameters ( γ iP ), derived from this study, are compared with the isothermal mode Grüneisen parameters ( γ iT ), calculated from the reported high-pressure measurements. The γ iP and γ iT parameters range from 0.46 to 3.43 for the lattice vibrational modes, whereas they are smaller than 0.4 for the internal vibrational modes of the CO 3 group, consistent with the CO 3 group serving as rigid bodies in the crystal structure. At high temperatures, the γ iP parameters for in-plane and out-of-plane bending modes are systematically smaller than those for asymmetric and symmetric stretching modes of CO 3 , implying that the O–C–O angles are even less sensitive to temperature than the C–O bond lengths. The intrinsic anharmonicities are also evaluated. The averaged anharmonic modes ( a i_avg ) are positive for cerussite, but negative for aragonite, strontianite and witherite. The intrinsic anharmonicity has quite different contributions to the equation of state and thermodynamic properties of cerussite, compared with other carbonate minerals, at the high temperatures and high pressures of mantle conditions.

Powder X-ray diffraction measurements were carried out on various samples to characterize their thermal expansion over a wide temperature range (93–1373 K). Using an effective interatomic potential model, we present a method to empirically estimate the Grüneisen parameter, as well as cubic and quartic anharmonic contributions to the lattice potential. This method is further tested on materials for which thermal expansion data are readily available. For most of the materials surveyed, the Grüneisen parameter values match those reported in the literature, obtained using traditional techniques. Thus, this work presents a novel and convenient Grüneisen parameter estimation method that uses measurements of only one physical property, thermal expansion.

High-temperature X-ray diffraction measurements of calcium ferrite (CF)-type MgAl 2 O 4 were performed in a temperature range of 300–673 K at atmospheric pressure. From temperature dependence of the unit cell volume, thermal expansivity ( α ) was determined to be α ( T ) = (2.46 ± 0.13) × 10 –5  + (1.2 ± 0.3) × 10 –8   T in 1/K. Thermoelastic parameters of isothermal bulk modulus at zero pressure ( K T 0 ), its pressure derivative ( K T ′) and temperature derivative [(∂ K T 0 /∂ T ) P ] of MgAl 2 O 4 CF were optimized by iteration calculation combining the least squares fitting of a third-order Birch–Murnaghan equation of state to previous P – V – T data with α calculation using the Grüneisen relation equation, α  =  γ th C V /( K T 0 V ) where γ th and C V are thermal Grüneisen parameter and isochoric heat capacity, respectively. γ th was constrained by the α measured in this study. When pressure data were rescaled by Au equations of state which are different from that adopted in the previous study and temperature data were corrected using pressure dependence of electromotive force of a W–Re thermocouple, K T 0 , K T ′ and (∂ K T 0 /∂ T ) P were assessed to be 216(4) GPa, 3.9(3) and − 0.027(3) GPa/K, respectively. It was suggested that the optimized α was about 17% lower than that determined by the previous study at 2000 K.

The ionic transport and the mechanical properties in solids are intimately related. However, few studies have been done to elucidate the background of that relation. With the objective to fill this gap and gain further understanding on the fundamental properties of ion conducting materials, we are studying systematically the mechanical properties of different materials. In the present study, after showing briefly our previous results obtained in crystalline materials, results regarding the relation between ionic conduction and mechanical properties in superionic glasses is presented. All these results indicate the intimate relation between the mechanical and ionic conduction. The results also indicate that the Grüneisen parameter and the Anderson–Grüneisen parameter of ionic conductors exhibit large temperature dependence and increase with temperature.