Pressure-volume Data Research Articles

Equation of state of theα−PbO2andPa3¯-type phases ofGeO2to 120 GPa

The compression behavior of crystalline and amorphous germania holds considerable interest as an analog for silica and for understanding the structural response of $\mathrm{A}{\mathrm{X}}_{2}$ compounds generally. In this paper, the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pb}{\mathrm{O}}_{2}$-type and $Pa\overline{3}$-type polymorphs of $\mathrm{Ge}{\mathrm{O}}_{2}$ were investigated under high pressure using angle-dispersive synchrotron x-ray diffraction in the laser-heated diamond anvil cell. Theoretical calculations based on density functional theory were also performed. The experimental pressure-volume data were fitted to third-order Birch-Murnaghan equations of state. The fit parameters for the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pb}{\mathrm{O}}_{2}$ type are ${V}_{0}=53.8\phantom{\rule{0.16em}{0ex}}(2)\phantom{\rule{0.16em}{0ex}}{\AA{}}^{3},{K}_{0T}=293\phantom{\rule{0.16em}{0ex}}(7)\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ with fixed ${K}_{0T}^{\ensuremath{'}}=4$, where $V,{K}_{T}$, and ${K}_{T}^{\ensuremath{'}}$ are the volume, isothermal bulk modulus, and pressure derivative of the bulk modulus and the subscript zero refers to ambient conditions. The corresponding parameters for the $Pa\overline{3}$-type phase are ${V}_{0}=50.3\phantom{\rule{0.16em}{0ex}}(3)\phantom{\rule{0.16em}{0ex}}{\AA{}}^{3},{K}_{0T}=342\phantom{\rule{0.16em}{0ex}}(12)\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ with fixed ${K}_{0T}^{\ensuremath{'}}=4$. The theoretical calculations are in good agreement with the experimental results with slight underestimation and overestimation of ${V}_{0}$ and ${K}_{0T}$, respectively. A theoretical Hugoniot was calculated from our data and compared to shock equation of state data for vitreous and rutile-type $\mathrm{Ge}{\mathrm{O}}_{2}$. The high-pressure phase observed on the Hugoniot is most consistent with either the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pb}{\mathrm{O}}_{2}$-type or $\mathrm{CaC}{\mathrm{l}}_{2}$-type phase. Finally, we have compared our data on crystalline germania with existing studies on the corresponding phases of $\mathrm{Si}{\mathrm{O}}_{2}$ to better understand the effects of cation substitution on phase transformations and equations of state in group 14 dioxides.

Real-time Pressure-volume Analysis of Acute Myocardial Infarction in Mice.

Acute myocardial infarction can lead to acute heart failure and cardiogenic shock. The evaluation of hemodynamics is critical for the evaluation of any potential therapeutic approach directed against acute left ventricular (LV) dysfunction. Current imaging modalities (e.g., echocardiography and magnetic resonance imaging) have several limitations since data on LV pressure cannot directly be measured. LV catheterization in mice undergoing coronary artery occlusion could serve as a novel method for a real-time evaluation of LV function. At the beginning of the procedure, mice were anesthetized followed by endotracheal intubation. For LV catheterization, the right carotid artery was exposed via middle-neck incision. The catheter was introduced and placed into the LV cavity. Left thoracotomy was conducted and the left main coronary artery (LCA) was ligated. To induce reperfusion, the suture was released after 45 min. Pressure-volume data was recorded at all times. Ligation of the LCA caused a decrease in LV systolic function as evidenced by a 30% reduction in stroke volume, LV ejection fraction (EF), and cardiac output. Maximum dP/dt as a parameter for LV contractility was also significantly reduced and diastolic function was severely impaired (minimum dP/dt -40%). Reperfusion over a period of 20 min did not lead to a complete recovery of LV function. Real-time pressure-volume analysis served as a valid procedure for monitoring cardiac function during acute myocardial infarction in mice. Maintaining stable anesthesia and a standardized surgical approach was crucial to ensure valid results. As the early phase of acute myocardial infarction is critical for morbidity and mortality, the delineated method could be beneficial for preclinical evaluation of new strategies for cardioprotection.

Copper Delafossites under High Pressure—A Brief Review of XRD and Raman Spectroscopic Studies

Delafossites, with a unique combination of electrical conductivity and optical transparency constitute an important class of materials with their wide range of applications in different fields. In this article, we review the high pressure studies on copper based semiconducting delafossites with special emphasis on their structural and vibrational properties by synchrotron based powder X-ray diffraction and Raman spectroscopic measurements. Though all the investigated compounds undergo pressure induced structural phase transition, the structure of high pressure phase has been reported only for CuFeO2. Based on X-ray diffraction data, one of the common features observed in all the studied compounds is the anisotropic compression of cell parameters in ambient rhombohedral structure. Ambient pressure bulk modulus obtained by fitting the pressure volume data lies between 135 to 200 GPa. Two allowed Raman mode frequencies Eg and A1g are observed in all the compounds in ambient phase with splitting of Eg mode at the transition except for CuCrO2 where along with splitting of Eg mode, A1g mode disappears and a strong mode appears which softens with pressure. Observed transition pressure scales exponentially with radii of trivalent cation being lowest for CuLaO2 and highest for CuAlO2. The present review will help materials researchers to have an overview of the subject and reviewed results are relevant for fundamental science as well as possessing potential technological applications in synthesis of new materials with tailored physical properties.

Compression behavior and phase transition of β-Si3N4 under high pressure

The compressibility and pressure-induced phase transition of β-Si3N4 were investigated by using an angle dispersive x-ray diffraction technique in a diamond anvil cell at room temperature. Rietveld refinements of the x-ray powder diffraction data verified that the hexagonal structure (with space group P63/m, Z = 2 formulas per unit cell) β-Si3N4 remained stable under high pressure up to 37 GPa. Upon increasing pressure, β-Si3N4 transformed to δ-Si3N4 at about 41 GPa. The initial β-Si3N4 was recovered as the pressure was released to ambient pressure, implying that the observed pressure-induced phase transformation was reversible. The pressure–volume data of β-Si3N4 was fitted by the third-order Birch–Murnaghan equation of state, which yielded a bulk modulus K0 = 273(2) GPa with its pressure derivative (fixed) and K0 = 278(2) GPa with . Furthermore, the compressibility of the unit cell axes (a and c-axes) for the β-Si3N4 demonstrated an anisotropic property with increasing pressure.

Revisiting ideal gases and proposal of a simple experiment for determining atmospheric pressure in the laboratory

Relevant historical aspects concerning ideal gases were briefly reviewed to provide a condensed resource for the undergraduate student of chemistry. The importance of the barometer and the concept of atmospheric pressure were reviewed and discussed. A combination of Boyle's law with the well-known equation for determining the pressure produced by a column of stationary fluid was used to obtain a graphical method for determining atmospheric pressure under isothermal conditions in the laboratory. Important aspects related to the study of ideal gases were reviewed in light of the pressure-volume data that can be obtained by physical chemistry students using a simple apparatus composed of a commercial hypodermic syringe connected to a mercury manometer. Relevant concepts associated with the measurement of a physical quantity, the importance of linear regression, as well as the use of a graphical method to test the validity of a theory were reviewed from a pedagogical perspective through the experimental study of Boyle's law during regular experimental physical chemistry classes.

Phase transition of intermetallic TbPt at high temperature and high pressure

Here we present synchrotron-based x-ray diffraction experiments combined with diamond anvil cell and laser heating techniques on the intermetallic rare earth compound TbPt (Pnma and Z = 4) up to 32.5 GPa and ~1800 K. The lattice parameters of TbPt exhibit continuous compression behavior up to 18.2 GPa without any evidence of phase transformation. Pressure–volume data were fitted to a third-order Birch–Murnaghan equation of state with V0 = 175.5(2) Å3, = 110(5) GPa and = 3.8(7). TbPt exhibits anisotropic compression with βa > βb > βc and the ratio of axial compressibility is 2.50:1.26:1.00. A new monoclinic phase of TbPt assigned to the Pc or P2/c space group was observed at 32.5 GPa after laser heating at ~1800 K. This new phase is stable at high pressure and presented a quenchable property on decompression to ambient conditions. The pressure–volume relationship is well described by the second-order Birch–Murnaghan equation of state, which yields V0 = 672(4) Å3, = 123(6) GPa, which is about ~14% more compressible than the orthorhombic TbPt. Our results provide more information on the structure and elastic property view, and thus a better understanding of the physical properties related to magnetic structure in some intermetallic rare earth alloys.

Pressure-induced transformations of multiferroic relaxor PbFe0.5Nb0.5O3

The effects of hydrostatic pressure at ambient temperature on the structural and dielectric properties of PbFe0.5Nb0.5O3 (PFN) were investigated using second harmonic generation (SHG) and powder x-ray diffraction measurements to 31 GPa. The results demonstrate that PFN undergoes a pressure-induced structural transition from the R3m ferroelectric to the R3¯m paraelectric phase. SHG measurements showed a continuous decrease in the signal with pressure and complete disappearance at 7.1 GPa. Effective nonlinear optical coefficients were determined from the SHG data, and their pressure behavior was used to infer the nature of the transition. The loss of the SHG signal is accompanied by drastic changes in line widths of Bragg reflections, but no discontinuous change in volume was observed. The pressure-volume data were fit to various equations of state, and a bulk modulus K0 = 136 (±2) GPa, bulk modulus pressure derivative K0′ = 4.0 (±0.2), and initial volume V0 = 64.5 (±0.1) Å3 were obtained.

Anomalous compression behaviour in Nd2O3 studied by x-ray diffraction and Raman spectroscopy

The structural stability of hexagonal Nd2O3 under pressure has been investigated by in situ synchrotron angle dispersive x-ray diffraction and Raman spectroscopy up to 53.1 GPa and 37.0 GPa, respectively. Rietveld analysis of the x-ray diffraction data indicate that the hexagonal Nd2O3 undergoes an isostructural phase transition in the pressure range from 10.2 to 20.3 GPa, accompanied by anomalous lattice compressibility and pressure-volume curve. A third-order Birch-Murnaghan fit based on the observed Pressure-Volume data yields zero pressure bulk moduli (B0) of 142(4) and 183(6) GPa for the low and high pressure hexagonal phases, respectively. Raman spectroscopy confirms this isostructural transition, the pressure dependence of the Raman modes display noticeable breaks in the pressure range of 9.7-20.9 GPa, which is consistent with the change of Nd-O bond length. The pressure coefficients of Raman peaks and the mode Grüneisen parameters of different Raman modes were also determined.

Observation of the negative pressure derivative of the bulk modulus in monoclinic ZrO2

Using synchrotron radiation x-ray diffraction techniques, the equation of state of monoclinic ZrO2 has been investigated under a hydrostatic pressure condition at 298 K. Monoclinic ZrO2 transformed to the orthorhombic I phase at between 5.7 and 7.0 GPa. Lattice constants of monoclinic ZrO2 refined from the Reitveld analysis showed extreme anisotropic pressure dependence. From the pressure–volume data, using least-squares fit of the Birch–Murnaghan formula, the bulk modulus, K0 and its pressure derivative: K0′, were estimated to be 159(3) GPa and −3.6(6), respectively. A negative K0′ suggests the abnormal softening of the elastic modulus in monoclinic ZrO2 with compression. First-principles calculations supported present experimental results.

High-pressure synchrotron x-ray diffraction and Raman spectroscopic study of plumbogummite**Project supported by the National Natural Science Foundation of China (Grant Nos. 41473056 and 41472037).

PbAl3(PO4)2(OH,H2O)6, an important environmental mineral, is in-situ studied by synchrotron x-ray diffraction (XRD) and Raman scattering combined with diamond anvil cells (DACs) at pressures up to ∼11.0 GPa and room temperature. The XRD results indicate that plumbogummite does not undergo a phase transition between 0 GPa and 10.9 GPa. Moreover, the c axis is more compressible than the a axis, revealing its anisotropic behavior. The pressure-volume data are fitted to the third-order Birch-Murnaghan equation of state to yield the plumbogummite bulk modulus of 68(1) GPa and of 6.1. The [PO4]3− and [HPO4]2− Raman vibrational modes exhibit scale nearly linearly as a function of pressure. The [PO4]3− stretching modes are generally more sensitive to pressure than the bending modes. The Grüneisen parameters range from −0.07 to 1.19, with an arithmetic mean of approximately 0.39.

X-ray Diffraction, Lattice Structure, and Equation of State of PdHx and PdDx to Megabar Pressures

High-pressure X-ray diffraction of PdHx and PdDx demonstrates that these materials remain in a face-centered cubic (fcc, Fm3̅m) structure to megabar pressures at room temperature. The volumes indicate stoichiometric compositions under pressure with x = 1 for both materials. No indication of any phase transition was observed up to the highest pressures reached in the experiments. A third-order Birch–Murnaghan equation of state used to fit the pressure–volume data gives V0 = 10.73 (±0.03) cm3/mol, K0 = 147 (±11) GPa, and K0′ = 4.7 (±0.5), whereas a Vinet fit gives V0 = 10.74 (±0.03) cm3/mol, K0 = 143 (±11) GPa, and K0′ = 5.1 (±0.5), for the combined data for both PdHx and PdDx. The results are used to obtain the pressure dependence of the effective volume of H and D atoms in PdHx and PdDx to megabar pressures for comparison with other simple hydrides with implications for superconductivity in this class of materials.

Pressure-induced polymorphism in hypervalent CsI3

We report the results of ambient temperature high-pressure synchrotron-based x-ray diffraction, Raman, and electrical resistance study of $\mathrm{Cs}{\mathrm{I}}_{3}$ up to 29, 25, and 8 GPa, respectively, and confirm three-phase transitions under quasihydrostatic conditions. The ambient orthorhombic (space group (SG): Pnma) phase of $\mathrm{Cs}{\mathrm{I}}_{3}$ is stable up to a pressure of $\ensuremath{\sim}1.3\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, above which a phase transition to a trigonal ($\mathrm{SG}:P\text{\ensuremath{-}}3c1$) phase is observed. The stability region of the trigonal phase has been found to be up to 22.6 GPa, above which the trigonal phase transforms to a cubic ($\mathrm{SG}:Pm\text{\ensuremath{-}}3n$) phase which remains stable until the maximum pressure of 29 GPa achieved in this study. A third-order Birch-Murnaghan equation of state fit to the pressure volume ($P\text{\ensuremath{-}}V$) data yields a bulk modulus of 17.7(9) GPa for the trigonal phase. Raman spectroscopic measurements however indicate three-phase transitions at $\ensuremath{\sim}1.3,\phantom{\rule{0.16em}{0ex}}4.0$, and 22.6 GPa, respectively. The electrical resistance measured in the low-pressure region up to 8 GPa indicates an electronic transition at around 4 GPa confirming the Raman result observed at 4.0 GPa. The $P\text{\ensuremath{-}}V$ data when transformed to the universal equation of state (UEOS) show a deviation from linearity around 4.0 GPa confirming the electronic transition. The present study has thus revealed a three-phase structural sequence in alkali trihalides, viz., orthorhombic (SG: Pnma) to trigonal ($\mathrm{SG}:P\text{\ensuremath{-}}3c1$) to a cubic ($\mathrm{SG}:Pm\text{\ensuremath{-}}3n$) phase.

High pressure structural phase transitions in Ho: Eu2O3

Structural stability and phase transitions in mixed rare earth sesquioxides (Eu1−xHox)2O3 crystallizing in the cubic bixbyite structure were investigated under high pressure using angle dispersive X-ray diffraction technique. Studies on various compositions of the mixed oxide show that when the average cationic radius, RRE (where, RRE = xRHo+(1−x)REu) is equivalent to or below 0.9164 Å, the system undergoes a cubic to monoclinic transition as a function of pressure, whereas, when RRE equivalent to or above 0.9220 Å it is observed to prefer a transition from cubic to hexagonal structure. Based on our detailed investigations, a pressure-concentration (P−x) phase diagram for (Eu1−xHox)2O3 up to a pressure of 15 GPa is constructed. The bulk moduli for the parent and high pressure phases are calculated from the Birch-Murnaghan equation of state fit to the experimental pressure volume data and are reported. Structural analysis based on refinement has revealed that, an increasing structural rigidity of the cubic phase with decreasing RRE leads to an increase in the transition pressure and bulk moduli except for 0.4 ≤ x ≤ 0.6. The observed significant reduction in bulk moduli and transition pressure for 0.4 ≤ x ≤ 0.6 is due to the increased micro strain/internal pressure developed upon doping.

Phase stability and incompressibility of tungsten boride (WB) researched by in-situ high pressure x-ray diffraction

The binary tungsten boride, WB, has potential industrial applications as it not only has a high melting point but is generally harder and less compressible than the pure metals. Here, the physical and mechanical properties (phase stability, bulk modulus and compressibility) of WB were investigated by in situ high-pressure x-ray diffraction and theoretical calculations. Its crystal structure still remains stable even at the highest pressure of 63.7GPa and room temperature for the diamond-anvil cell experiments. The pressure-volume (P-V) data were fitted using the Birch-Murnaghan EOS and the Vinet EOS to obtain the isothermal bulk modulus, K0 = 452 (4) GPa and 451(3) GPa and its pressure derivative, K0′ = 4 (fixed) in the two sets of experiments with two different pressure transmitting mediums (PTMs), respectively. The excellent bulk modulus (K0) is attributed to the high valence electron density of W atom, the layered and chain-like crystal structure of WB and the strong chemical bonds formed by W and B atoms. Besides, anisotropic compression behavior of the unit-cell axes (a- and c-axes) of WB is manifested by experimental observations and theoretical calculations. This remarkably elastic property is closely related to the strongly directional bonding between W and B atoms.

Pressure-Driven Isostructural Phase Transition in InNbO4: In Situ Experimental and Theoretical Investigations.

The high-pressure behavior of technologically important visible-light photocatalytic semiconductor InNbO4, adopting a monoclinic wolframite-type structure at ambient conditions, was investigated using synchrotron-based X-ray diffraction, Raman spectroscopic measurements, and first-principles calculations. The experimental results indicate the occurrence of a pressure-induced isostructural phase transition in the studied compound beyond 10.8 GPa. The large volume collapse associated with the phase transition and the coexistence of two phases observed over a wide range of pressure shows the nature of transition to be first-order. There is an increase in the oxygen anion coordination number around In and Nb cations from six to eight at the phase transition. The ambient-pressure phase has been recovered on pressure release. The experimental pressure-volume data when fitted to a Birch-Murnaghan equation of states yields the value of ambient pressure bulk modulus as 179(2) and 231(4) GPa for the low- and high-pressure phases, respectively. The pressure dependence of the Raman mode frequencies and Grüneisen parameters was determined for both phases by experimental and theoretical methods. The same information is obtained for the infrared modes from first-principles calculations. Results from theoretical calculations corroborate the experimental findings. They also provide information on the compressibility of interatomic bonds, which is correlated with the macroscopic properties of InNbO4.

Anomalous lattice compressibility of hexagonal Eu2O3

Monoclinic Eu2O3 was investigated in a Mao-Bell type diamond anvil cell using angle dispersive x-ray diffraction up to a pressure of 26 GPa. Pressure induced structural phase transition from monoclinic to hexagonal phase was observed at 4.3 GPa with 2% volume collapse. Birch –Murnaghan equation of state fit to the pressure volume data yielded a bulk modulus of 159(9) GPa and 165(6) GPa for the monoclinic and hexagonal phases respectively. Equation of state fitting to the structural parameters yielded an axial compressibility of βa > βc > βb for the parent monoclinic phase, showing the least compressibility along b axis. Contrary to the available reports, an anomalous lattice compressibility behavior is observed for the high pressure hexagonal phase, characterized by pronounced hardening of a axis above 15 GPa. The observed incompressible nature of the hexagonal a axis in the pressure range 15–25 GPa is found to be compensated by doubling the compressibility along the c axis.

Thermo-elastic behavior of grossular garnet at high pressures and temperatures

The thermo-elastic behavior of synthetic single crystals of grossular garnet (Ca 3 Al 2 Si 3 O 12 ) has been studied in situ as a function of pressure and temperature separately. The same data collection protocol has been adopted to collect both the pressure-volume ( P-V ) and temperature-volume ( T-V ) data sets to make the measurements consistent with one another. The consistency between the two data sets allows simultaneous fitting to a single pressure-volume-temperature Equation of State (EoS), which was performed with a new fitting utility implemented in the latest version of the program EoSFit7c. The new utility performs fully weighted simultaneous fits of the P-V-T and P-K-T data using a thermal pressure EoS combined with any P-V EoS. Simultaneous refinement of our P-V-T data combined with that of K T as a function of T allowed us to produce a single P-V-T-K T equation of state with the following coefficients: V 0 = 1664 . 46 ( 5 ) A 3 , K T 0 = 166 . 57 ( 17 ) GPa and K ′ = 4 . 96 ( 7 ) α ( 300 K , 1 bar ) = 2 . 09 ( 2 ) × 10 − 5 K − 1 with a refined Einstein temperature (θ E ) of 512 K for a Holland-Powell-type thermal pressure model and a Tait third-order EoS. Additionally, thermodynamic properties of grossular have been calculated for the first time from crystal Helmholtz and Gibbs energies, including the contribution from phonons, using density functional theory within the framework of the quasi-harmonic approximation.

MP46-14 INVALIDATION OF THE PRACTICE OF ADDING FLUID TO THE AMS 800 ARTIFICIAL URINARY SPHINCTER PRESSURE REGULATING BALLOON

You have accessJournal of UrologyUrodynamics/Lower Urinary Tract Dysfunction/Female Pelvic Medicine: Male Incontinence: Therapy1 Apr 2017MP46-14 INVALIDATION OF THE PRACTICE OF ADDING FLUID TO THE AMS 800 ARTIFICIAL URINARY SPHINCTER PRESSURE REGULATING BALLOON Zachary Koloff, Paholo Barboglio Romo, Yooni Yi, and Bahaa Malaeb Zachary KoloffZachary Koloff More articles by this author , Paholo Barboglio RomoPaholo Barboglio Romo More articles by this author , Yooni YiYooni Yi More articles by this author , and Bahaa MalaebBahaa Malaeb More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2017.02.1453AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES The artificial urinary sphincter (AUS) AMS 800 has proven to be very effective in treatment of stress urinary incontinence. However, surgeon practice patterns vary when the device does not provide the desired degree of dryness. A common approach utilized is to add additional fluid to the pressure regulating balloon (PRB). The goal of this study was to evaluate changes in pressure with the addition of fluid to the PRB. METHODS Ex vivo pressure studies were conducted on Boston Scientific AMS 800 PRBs rated 51-60, 61-70 and 71-80 cmH2O in a controlled laboratory setting using the Laborie Aquarius TT urodynamics system. After calibration of the equipment and appropriate cycling of the balloons in a standardized technique similar to that performed in the operating room setting, PRBs were initially filled to 10mL using 0.9% normal saline and opening pressures were obtained. We reported mean and standard deviation. Balloons were inflated up to 35 mL and pressure-volume data sets were acquired for each device. RESULTS The mean opening pressures at 10 mL fill volumes of the 51-60, 61-70, and 71-80 cmH2O PRBs were 51.0±4.8, 65.1±7.8, and 78.9±3.9 cmH2O, respectively. The pressure-volume curves appeared similar for all PRBs and rose to maximum pressures of 67.0±4.0, 87.3±5.1 and 105.7±2.4 cmH2O at fill volumes of 16, 17 and 16 mL, respectively for each type of PRB. The addition of any more volume to the balloons did not result in any additional increase in pressure up to a fill volume of 35 mL (see Figure 1). Following data collection, we continue filling the balloons to a volume of 500 mL. Even at these supra-physiologic volumes, pressures remained stable and only started slowly increasing to 100, 105 and 110 cmH2O respectively at 1 liter. CONCLUSIONS The AUS PRB is a very compliant device and adding more fluid to an in situ AUS PRB does not increase the pressure of the system. Although our study does not account for in vivo behavior within a possible capsule formation, we discourage this surgeon practice and recommend adopting a different corrective method for persistent urinary incontinence. © 2017FiguresReferencesRelatedDetails Volume 197Issue 4SApril 2017Page: e624-e625 Advertisement Copyright & Permissions© 2017MetricsAuthor Information Zachary Koloff More articles by this author Paholo Barboglio Romo More articles by this author Yooni Yi More articles by this author Bahaa Malaeb More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Anomalous Compressibility and Amorphization in AlPO4-17, the Oxide with the Highest Negative Thermal Expansion

AlPO4-17, known as the oxide with the highest negative thermal expansion (NTE), was studied under high pressure by angle-dispersive X-ray diffraction (XRD), mid- and far-infrared (IR) spectroscopy. Upon increasing pressure, the closure of the (P–O–Al) angle destabilizes the porous AlPO4-17 structure, which drives the amorphization process. On the basis of the decrease in intensity of the XRD lines and broadening of the IR modes, the material was found to begin to amorphize near 1 GPa. XRD, mid- and far-IR analysis evidenced pressure-induced framework softening and complete irreversible amorphization near 2.5 GPa corresponding to the collapse of the pores. The bulk modulus and its first pressure derivative (B0 = 31.2(5) GPa and B′0 = −10.1(3)) at ambient temperature were determined by fitting a third order Birch–Murnaghan equation of state (EOS) to the pressure–volume data. The material is extremely compressible and exhibits an elastic instability. Anomalous (negative) values of B′0 are very rare and have ...

Effect of three-body interactions on the zero-temperature equation of state of HCP solid 4He

Previous studies have pointed to the importance of three-body interactions in high density 4He solids. However the computational cost often makes it unfeasible to incorporate these interactions into the simulation of large systems. We report the implementation and evaluation of a computationally efficient perturbative treatment of three-body interactions in hexagonal close packed solid 4He utilizing the recently developed nonadditive three-body potential of Cencek et al. This study represents the first application of the Cencek three-body potential to condensed phase 4He systems. Ground state energies from quantum Monte Carlo simulations, with either fully incorporated or perturbatively treated three-body interactions, are calculated in systems with molar volumes ranging from 21.3 cm3/mol down to 2.5 cm3/mol. These energies are used to derive the zero-temperature equation of state for comparison against existing experimental and theoretical data. The equations of state derived from both perturbative and fully incorporated three-body interactions are found to be in very good agreement with one another, and reproduce the experimental pressure-volume data with significantly better accuracy than is obtained when only two-body interactions are considered. At molar volumes below approximately 4.0 cm3/mol, neither two-body nor three-body equations of state are able to accurately reproduce the experimental pressure-volume data, suggesting that below this molar volume four-body and higher many-body interactions are becoming important.