Showing papers in "High Pressure Research in 2006"
TL;DR: The conditions and mechanism of the formation of nano-polycrystalline diamond from graphite and non-graphitic carbon at high pressure and high temperature have been investigated in this article.
Abstract: The conditions and mechanism of formation of nano-polycrystalline diamonds directly from graphite and non-graphitic carbon (carbon black, glassy carbon, C60 and carbon nanotubes) at high pressure and high temperature have been investigated. The onset temperature for diamond formation at P≥q 15 GPa is 1500–1600 °C for all carbon materials, although the required temperature conditions for pure polycrystalline diamond are T≥q 2200 °C for graphite and T≥q 1600 °C for non-graphitic carbon. Polycrystalline diamond forms as a result of simultaneous diffusion and two-step martensitic processes from graphite, whereas it forms only due to diffusion without graphitization or formation of intermediate phases from non-graphitic carbon. Nano-polycrystalline diamonds consisting only of very fine particles (<10 nm in size) can be obtained from non-graphitic carbon at T∼ 1600–2000 °C under pressures≥q15 GPa.
71 citations
TL;DR: In this article, the application of high hydrostatic pressure (HHP) processing of food to extracting lycopene from tomato paste waste was studied and the experimental results of HHP showed that more Lycopene can be extracted from tomato waste in only 1min at room temperature without any heating process.
Abstract: The application of high hydrostatic pressure (HHP) processing of food to extracting lycopene from tomato paste waste was studied. Various experimental conditions of HHP processing process, such as solvents (chloroform, 95% ethanol and distilled water), ethanol concentration (45–95%, v/v), pressure (100–600 MPa), duration (1–10 min) and solid/liquid ratio (1:1 to 1:8 g/ml), were investigated to optimize the extraction process. The experimental results of HHP showed that more lycopene can be extracted from tomato paste waste in only 1 min at room temperature without any heating process. The highest recovery (92%) was obtained by performing the extractions at 500 MPa pressure, 1 min duration, 75% ethanol concentration, and 1:6 (g/ml) solid/liquid ratio. From the viewpoints of extraction time, the extraction yield and the extraction efficiency, extraction by HHP shows a bright prospect for extracting lycopene from tomato paste waste.
55 citations
TL;DR: In this paper, the stability of CH4, CH6, CH8H18, DECANE, octane, decane, octadecane (C18H38), and non-decane was studied in a CO2-laser heated diamond anvil cell at pressures up to 25 GPa and temperatures up to about 7300 K. Methane and ethane were found to decompose to hydrogen and diamond.
Abstract: The stability of methane (CH4), ethane (C2H6), octane (C8H18), decane (C10H22), octadecane (C18H38), and nonadecane (C19H40) were studied in a CO2-laser heated diamond anvil cell at pressures up to 25 GPa and temperatures up to about 7300 K. Methane and ethane were found to decompose to form hydrogen and diamond. Substantially greater yields of diamond were obtained from the longer chain alkanes.
51 citations
TL;DR: In this article, high-purity polycrystalline cBN (pcBN) has been obtained from bulk pyrolytic graphite-like BN at a pressure of about 8 GPa and temperatures of 2500 and 2800 K. The size of grains in the sample produced at 2500 K ranged from 100 to 400nm.
Abstract: High-purity polycrystalline cBN (pcBN) has been obtained from bulk pyrolytic graphite-like BN at a pressure of about 8 GPa and temperatures of 2500 and 2800 K. The size of grains in the sample produced at 2500 K ranged from 100 to 400 nm. The formation of the fine-grained structure has given rise to an increase in both hardness and fracture toughness of pure pcBN when compared with cBN single crystals (s.c.), the elastic modulus is close in value to the elastic modulus of s.c. High mechanical characteristics of the sample produced at 2500 K are caused by a grain small size and pure dense grain boundaries of the recrystallization origin. The increase in the synthesis temperature to 2800 K results in an abrupt decrease in hardness because of the grain size growth in the course of the collective recrystallization.
50 citations
TL;DR: The first alkali metal to become superconducting under high pressure is Cs followed years later by Li as mentioned in this paper, which is surprising and is a result of the fact that under pressure it shows marked deviations from free-electron behaviour where, counterintuitively, bands narrow and gaps widen.
Abstract: At ambient pressure there are 29 elemental superconductors in the periodic table, none of which is an alkali metal. The first alkali metal to become superconducting under high pressure is Cs followed years later by Li. Alkali metals are believed to be exemplary free-electron systems. The fact that an alkali metal becomes superconducting at all is surprising and is a result of the fact that under pressure it shows marked deviations from free-electron behaviour where, counterintuitively, bands narrow and gaps widen. For this reason the alkali metals are among the most interesting systems known to study in high-pressure experiments and superconductivity is one of their most fascinating properties.
38 citations
TL;DR: In this paper, the melting temperature, T m, of copper was determined from ambient pressure to 16 GPa using multi-anvil techniques and the melting curve obtained (T m=1355(5)+44.5(31)P−0.61(21)P 2, with T m in Kelvin and P in GPa) is in good agreement with both the previous experimental studies and with recent ab initio calculations.
Abstract: The melting temperature, T m, of copper has been determined from ambient pressure to 16 GPa using multi-anvil techniques. The melting curve obtained (T m=1355(5)+44.5(31)P−0.61(21)P 2, with T m in Kelvin and P in GPa) is in good agreement with both the previous experimental studies and with recent ab initio calculations.
37 citations
TL;DR: In this paper, the authors performed high-pressure Hall effect and resistivity measurements in p-type GaSe and InSe up to 12 GPa and found that hole concentration and mobility increase moderately and continuously.
Abstract: We performed high-pressure Hall effect and resistivity measurements in p-type GaSe and InSe up to 12 GPa. The pressure behaviour of the transport parameters shows dramatic differences between both materials. In GaSe, the hole concentration and mobility increase moderately and continuously. In InSe, the hole mobility raises rapidly and the hole concentration increases abruptly near 0.8 GPa. The observed results are attributed to the different pressure evolution of the valence-band structure in each material. In InSe a carrier-type inversion is also detected near 4.5 GPa.
27 citations
TL;DR: In this paper, the authors measured compressibilities measured by synchrotron X-ray diffraction and phonon spectra from Raman scattering at high pressure in the diamond anvil cell (DAC) for cubic transition metal nitrides TiN1−x, γ-Mo2N and VN x.
Abstract: We report compressibilities measured by synchrotron X-ray diffraction and phonon spectra from Raman scattering at high pressure in the diamond anvil cell (DAC) for cubic transition metal nitrides TiN1−x , γ-Mo2N and VN x . The high-hardness metal nitride compounds have large values of the bulk modulus. B1-structured nitrides normally have no allowed first-order Raman spectra. However, they exhibit broad bands that reflect the vibrational density of states g(ω) associated with breakdown of q=0 selection rules because of the presence of N3− vacancies on anion sites. Peaks in g(ω) at low frequency are identified with the longitudinal and transverse acoustic (TA) branches. The maximum in the TA band is correlated with the superconducting transition temperature in these materials (T c). In situ Raman scattering measurements in the DAC thus permit predictions of the T c variation with pressure for cubic nitrides and isostructural carbide materials.
27 citations
TL;DR: The experimental bulk modulus is 25(5) GPa for the orthorhombic phase of L-alanine as discussed by the authors, which is the same as that of the standard L-alane.
Abstract: L-ALANINE has been studied by X-ray diffraction at ambient temperature and pressure up to 10.3 GPa. The material is found to transform to a tetragonal structure between 2 and 3 GPa and to a monoclinic structure between 8 and 10 GPa. The experimental bulk modulus is 25(5) GPa for the orthorhombic phase. The results are compared with previous measurements of L-ALANINE.
24 citations
TL;DR: In this article, the authors studied the effect of stress demagnetization on magnetite under quasi-hydrostatic loads in the presence of a small Earth's magnetic field and concluded that the presence or absence of a planetary magnetic field cannot be deduced from the magnetic fields measured over meteorite craters, such as those on Mars.
Abstract: Stress demagnetization effects on ferromagnetic minerals are poorly known, especially above 1 GPa, and when initially magnetized under pressure and then subjected to further stress. Our experiments on pure magnetite under quasi-hydrostatic loads in the presence of a small (Earth’s) field show that stress demagnetization depends on domain state and stress history. Viewed globally, the results follow a simple law where the percentage loss in magnetic moment is the inverse of pressure (e.g., 50% loss in moment at 1 GPa, 67% loss at 2 GPa, etc.). Our experiments also quantify the effect of demagnetization upon stress release, where the moment upon full decompression is two-thirds less than the moment when decompression first began. Given the magnitude of the stress demagnetization effect, we conclude that the presence or absence of a planetary magnetic field cannot be deduced from the magnetic fields measured over meteorite craters, such as those on Mars.
24 citations
TL;DR: In this article, both energy-dispersive (EDX) and angle-disperive (ADX) X-ray diffraction methods were performed at the BL04B1 beamline of SPring8 (Japan) and at the ID27-30 beamline (France) respectively.
Abstract: The high-pressure melting behavior of different iron alloys was investigated using the classical synchrotron-based in situ X-ray diffraction techniques. As they offer specific advantages and disadvantages, both energy-dispersive (EDX) and angle-dispersive (ADX) X-ray diffraction methods were performed at the BL04B1 beamline of SPring8 (Japan) and at the ID27-30 beamline of the ESRF (France), respectively. High-pressure vessels and pressure ranges investigated include the Paris- Edinburgh press from 2 to 17GPa, the SPEED-1500 multi-anvil press from 10 to 27 GPa, and the laser-heated diamond anvil cell from 15 to 60 GPa. The onset of melting (at the solidus or eutectic temperature) can be easily detected using EDX because the grains start to rotate relative to the X-ray beam, which provokes rapid and drastic changes with time of the peak growth rate. Then, the degree of melting can be determined, using both EDX and ADX, from the intensity of diffuse X-ray scattering characteristic of the liquid phase. This diffuse contribution can be easily differentiated from the Compton diffusion of the pressure medium because they have different shapes in the diffraction patterns. Information about the composition and/or about the structure of the liquid phase can then be extracted from the shape of the diffuse X-ray scattering.
TL;DR: In this paper, a new series of high pressure cells for in situ multi-anvil experiments is described, which are based on the conventional COMPRES cells, but modifications are made to improve the passage of X-rays.
Abstract: A new series of high-pressure cells for in situ multi-anvil experiments is described. The cells are based on the conventional COMPRES cells, but modifications are made to improve the passage of X-rays. The modifications include cutting slits in parts of the assemblies that have very high X-ray absorption, such as lanthanum chromite and rhenium, the use of low-Z thermal insulation, such as forsterite, in place of zirconia, and the partial replacement of zirconia by MgO equatorial windows combined with a mullite octahedron. Details of the designs, thermal characterizations, and examples of the application of these cells are described.
TL;DR: In this article, an ab initio analysis of pressure-induced metallization of methane is presented, and it is shown that it is not predicted to occur below 520 GPa, which corresponds to a compression factor of 7.5.
Abstract: Recently reported superconductivity in lithium under pressure has renewed the interest in hydrogen and hydrogen-rich systems in the long standing quest for room temperature superconductivity. As the required metallization of pure hydrogen cannot be achieved within current experimental capabilities, it has been suggested that the chemical precompression exerted by heavier atoms in compounds with a large hydrogen content should lower the required pressures to attain the metallic transition in these alloys. Following the trend of analyzing group IVa hydrides, we present an ab initio analysis of pressure-induced metallization of methane. According to our calculations, the metallization of methane is not predicted to occur below 520 GPa, which corresponds to a compression factor of 7.5.
TL;DR: In this paper, the hydrogen solubility of liquid water, hexagonal ice, and cubic clathrate ice was studied at hydrogen pressures up to 1.8 kbar and temperatures from −36 to +20 kC.
Abstract: Using a volumetric technique, the hydrogen solubility X in liquid water (L), low-pressure hexagonal ice (I h), and high-pressure cubic clathrate ice (sII) is studied at hydrogen pressures up to 1.8 kbar and temperatures from−36 to+20 °C. The triple point of the L+I h+sII equilibrium is located at P=1.07(5) kbar and T=−10(1) °C. The hydrogen concentrations of phases at the triple point are X L =0.17(5), and X sII=2.3(1) wt.% H2. The thermal stability and the process of decomposition of the clathrate phase at ambient pressure are studied by neutron diffraction.
TL;DR: In this article, the diamond anvil cell (DAC) at very high pressure has been used to yield data on a range of orientationdependent properties such as thermal and electrical conductivity, magnetic susceptibility, elasticity and plasticity.
Abstract: To date, most research utilizing the diamond anvil cell (DAC) at very high pressure has been conducted with polycrystalline samples, thus the results are limited to addressing average bulk properties. However, experiments on single crystals can yield data on a range of orientation-dependent properties such as thermal and electrical conductivity, magnetic susceptibility, elasticity and plasticity. Here, we report new procedures to produce extremely high-quality metallic single crystal samples of size compatible with DAC experiments in the Mbar range. So far, we have produced samples of zinc, Al2O3, cobalt, molybdenum and cerium, and have evaluated the quality of the finished samples with white-light interferometry, synchrotron X-ray diffraction and inelastic X-ray scattering.
TL;DR: In this paper, a new X-ray system was installed at the Bayerisches Geoinstitut for single-crystal structural studies on example of garnet, Co3Al2Si3O12.
Abstract: Newly installed, at Bayerisches Geoinstitut, X-ray system consists of three major components: RIGAKU FR-D high-brilliance source, Osmic's Confocal Max-Flux optics, and SMART APEX 4K CCD area detector. We tested the system for single-crystal structural studies on example of garnet, Co3Al2Si3O12, for powder diffraction analysis on example of a small sample of boron carbide, B4C, recovered after treatment in a multi-anvil apparatus, and for in situ experiments at high pressure on example of FeO compressed in a diamond anvil cell to>100 GPa. In all the cases, the system demonstrated its reliability and provided results comparable with those obtained using the best currently available instruments. Using a new X-ray system, we measured the compressibility of superhard nanocrystalline diamond at pressures up to 26 GPa and found it to be extremely incompressible with K T=488(4) GPa, K′=3.1(2), and V 0=3.401(6) cm3/mol.
TL;DR: In this article, optical properties of the SrWO4 matrix doped with different Eu3+ concentrations (10, 13% and 20%) have been studied at ambient pressure, the temporal evolution of the emissions from the 5D1 level has been analyzed in the different doped crystals in order to discuss the energy transfer processes between the Eu 3+ ions.
Abstract: Optical properties of the SrWO4 matrix doped with different Eu3+ concentrations (10%, 13% and 20%) have been studied. At ambient pressure, the temporal evolution of the emissions from the 5D1 level has been analyzed in the different doped crystals in order to discuss the energy transfer processes between the Eu3+ ions. This study lets conclude that the Eu3+ ions are randomly distributed in the matrix. Moreover, the 5D0→7F1, 2 emissions have been measured increasing the pressure up to 15 GPa in order to analyze the changes in the Eu3+ local structure. The results confirm the existence of a structural phase transition around 8.5 GPa.
TL;DR: In this article, the high pressure behavior of fibrous zeolites scolecite and thomsonite was studied using in situ synchrotron powder diffraction data from diamond anvil cell.
Abstract: The high-pressure behaviour of fibrous zeolites scolecite and thomsonite in penetrating aqueous medium was studied using in situ synchrotron powder diffraction data from diamond anvil cell. Both zeolites exhibit anomalous compressibility due to an additional pressure-induced hydration of structure channels. At 1.23 GPa, scolecite undergoes transformation to high-hydrated phase, which is expanded by 5.0% as compared to original scolecite due to the increase of zeolitic water content from 3 to 4.6 molecules per formula unit. The compressibility of thomsonite is markedly lower than that reported previously, where a nominally penetrating medium with 6% H2O was used. This indicates to an additional hydration under high pressure, which is confirmed by the observed phase transition in thomsonite. The over-hydration effect in fibrous zeolites seems to largely depend on partial water pressure in compressing medium.
TL;DR: In this article, a multi-anvil assembly and modified gasket characteristics with octahedron and truncation edge lengths of 10 and 3.5mm is presented for reaching pressures and temperatures over 24 GPa and 2000 C, respectively.
Abstract: A new design of multi-anvil assembly and modified gasket characteristics with octahedron and truncation edge lengths of 10 and 3.5 mm is presented for reaching pressures and temperatures over 24 GPa and 2000 °C, respectively. Partially dehydroxylated pyrophyllite half-gaskets with a tapered design fully nesting the octahedron have been employed to prevent excessive octahedron extrusion between the cubes. The assembly utilizes an axially placed thermocouple through the octahedral center, allowing two samples to be present at identical high P–T conditions on either side of the thermocouple during a run. A third sample can be used as a packing around the thermocouple, so long as that sample is inert with respect to the thermocouple and surrounding material. The temperature gradient within the sample locations has been well characterized using two-pyroxene thermometry in the CaO–MgO–SiO2 system and numerical modeling calculations. The results indicate a good agreement in gradient shape, although the numerical...
TL;DR: In this article, a high-pressure Raman study was carried out on NaA1H(4) up to 17 GPa using the diamond anvil cell method and several of the original modes split.
Abstract: A high-pressure Raman study was carried out on NaA1H(4) up to 17 GPa using the diamond anvil cell method. In the pressure region 2-5 GPa, several of the original modes split. Although this might be ...
TL;DR: In this article, the authors applied nanoindentation to synthetic diamond crystals, a chemical vapour deposition (CVD) grown diamond film and to aggregated diamond nanorods produced by high-pressure compression of fullerite.
Abstract: Nanoindentation is applied to synthetic diamond crystals, a chemical vapour deposition (CVD) grown diamond film and to aggregated diamond nanorods produced by high-pressure compression of fullerite. Characteristic load–displacement curves are used to determine the mechanical properties and to classify these materials. Atomistic simulations have also been carried out. The results show that diamond undergoes a mainly elastic deformation during nanoindentation. Both simulations and experiments show that the force exerted on the indenter varies as the depth raised to the power 1.6. Results for the CVD grown diamond films give smaller hardness values than for the diamond crystals. For the diamond nanorods sample, hardness values lie up to those determined for diamond, whereas the elastic modulus can exceed the diamond value.
TL;DR: In this paper, the complete sequence of hcp→Sm-type→dhcp→fcc→dfcc (hR24) is observed for the first time with transitions at 10, 19, 54, and 58 GPa, respectively.
Abstract: Pressure-induced structural phase transformations in heavy rare earth holmium have been studied in a diamond anvil cell using energy dispersive X-ray diffraction at a synchrotron source to pressures of 62 GPa at ambient temperature. The complete sequence of hcp→Sm-type→dhcp→fcc→dfcc (hR24) is observed for the first time with transitions at 10, 19, 54, and 58 GPa, respectively. The fcc phase is not observed as a pure phase. Each phase transition is correlated to predicted changes in d-band occupation at high pressure. As with many other rare earths, the regions of stability of the several phases are observed to overlap, and significant hysteresis is observed. The measured volume compression for Ho is V/V 0=0.526 at 62 GPa.
TL;DR: In this paper, a new variant of the method of finding the equation of state in the Mie-Gruneisen form is presented, based only on high-pressure isotherms of solids.
Abstract: A new variant of the method of finding the equation of state in the Mie–Gruneisen form is presented. It is based only on high-pressure isotherms of solids. Using this procedure, the semiempirical equation of state and shock adiabats of solids may be found at high pressures and high temperatures. The method is tested on periclase MgO within the range of shock pressures up to 300–500 GPa.
TL;DR: In this article, the authors studied the dependence of the emission bands and the lifetimes of the metastable 4F3/2 state of Nd3+ on hydrostatic pressure, which is a powerful technique to study the influence of the changing strength of the crystal field on the spectroscopic properties of luminescent centers in crystals.
Abstract: Optical properties of Nd3+-doped MgO:LiNbO3 have been intensively studied during the last years because of its potential applications as a multifunctional non-linear laser system capable, for example, of multi-frequency laser light generation. In order to exploit fully the advantages of this system, a complete knowledge of its excited state dynamics is required. The application of high-hydrostatic pressure is a powerful technique to study the influence of the changing strength of the crystal field on the spectroscopic properties of luminescent centers in crystals. We have studied the dependence of the emission bands and the lifetimes of the metastable 4F3/2 state of Nd3+ on hydrostatic pressure.
TL;DR: In this paper, the authors presented the results on the elastic wave velocities at the non-quenchable high-P-low-P clinoenstatite transition and on some innovative experiments to improve the potentials of multi-anvil apparatus in terms of maximum pressure.
Abstract: The Earth's mantle has a mass of about 4.08×1021 ton and represents 68% of the total mass of the Earth. The Earth's mantle is only accessible by indirect methods, such as seismological studies. The interpretation of seismic data from the Earth's deep interior requires measurements of the physical properties of Earth materials under experimental simulated mantle conditions. MAX80, maximum conditions of about 12 GPa/2000 K, and the sister apparatus MAX200x, designed to reach 25 GPa and 2400 K, are installed at HASYLAB beamlines. Both apparatus are equipped for XRD with a Ge-solid-state detector, for transient ultrasonic interferometry, as well as with a radiography system to measure the change of volume and shape of the sample under in situ conditions. Some recent results on the elastic wave velocities at the non-quenchable high-P–low-P clinoenstatite transition and on some innovative experiments to improve the potentials of multi-anvil apparatus in terms of maximum pressure are presented.
TL;DR: In this article, the physical and mechanical properties of a C60 fullerene sample have been investigated under high pressure-high temperature conditions using a diamond anvil cell, and the results indicated that the characteristic fcc reflections gradually decrease in intensity and eventually disappear above 28 GPa.
Abstract: The physical and mechanical properties of a C60 fullerene sample have been investigated under high pressure–high temperature conditions using a designer Diamond Anvil Cell. Electrical resistance measurements show evidence of C60 cage collapse at 20 GPa, which leads to the formation of an insulating phase at higher pressure. Energy dispersive X-ray diffraction (EDXD) data indicated that the characteristic fcc reflections gradually decrease in intensity and eventually disappear above 28 GPa. A C60 sample was laser-heated at a pressure of 35 GPa to a temperature of 1910±100 K and, subsequently, decompressed to ambient conditions. The photoluminescence spectra and the Raman spectrum of the pressure–temperature-treated sample were measured at a low temperature of 80 K. Raman peak at 1322.3 cm−1 with full-width half-maximum of 2.9 cm−1 was observed from the sample, which is attributed to the hexagonal diamond phase in the sample. The room temperature photoluminescence spectra showed a symmetric emission band ce...
TL;DR: In this article, the authors report on the state-of-the-art of the research carried out during past few years with the diamond anvils carrying implanted electronic structures (iAnvils).
Abstract: Since a long time, efforts have been made to improve the accuracy of pressure and temperature measurements in diamond anvil cell experiments performed in experimental petrology and high-pressure physics. Here, we report on the state-of-the-art of the research carried out during past few years with the diamond anvils carrying implanted electronic structures (‘intelligent’ anvils, iAnvils). The electronic structures are inserted a few microns below the diamond surface into the diamond lattice by high-energy implantation of boron. These structures can be used as pressure- and temperature-sensitive devices. Another useful application is the fabrication of micro-heaters integrated in the anvils. Pressure- and temperature-induced responses of the sensors (change of resistance) are quantified by low-current measurement equipment. Calibrations against pressure–temperature parameters are performed using well-known phase transitions or by using equation of state of pure substances. Results of in situ measurements p...
TL;DR: In this paper, an internally heated autoclave, modified in order to allow in situ studies at pressure up to 0.5 GPa and temperature up to 1000°C, is presented.
Abstract: We present an internally heated autoclave, modified in order to allow in situ studies at pressure up to 0.5 GPa and temperature up to 1000°C. It is equipped with transparent sapphire windows, allowing the observation of the whole experiment along the horizontal axis. In the experimental cell the sample is held between two thick transparent plates of sapphire or diamond, placed in the furnace cylinder. The experimental volume is about 0.01 cm3. Video records are made during the whole experiment. This tool is developed mainly to study magmatic processes, as the working pressures and temperatures are appropriate for subvolcanic magma reservoirs. However other applications are possible such as the study of subsolidus phase equilibria as we have used well known phase transitions, such as the system of AgI, to calibrate the apparatus with respect to pressure and temperature. The principle of the apparatus is detailed. Applications are presented such as studies of melt inclusions at pressure and temperature and an in situ study of magma degassing through the investigation of nucleation and growth processes of gas bubbles in a silicate melt during decompression.
TL;DR: In this paper, the pre-edge features have been used to determine the local distortion around the Ti atom as a function of applied features, and it is shown that at room pressure SrTiO3 was locally ferroelectric.
Abstract: The Ti K edge X-ray absorption has been measured under high pressure at room temperature for ATiO3 perovskites (A = Ca, Sr, Ba and Pb). The pre-edge features have been used to determine the local distortion around the Ti atom as a function of applied features. The ferroelectric local instability decreases when pressure is increased (PbTiO3) and eventually vanishes at high pressure (BaTiO3). The antiferrodistorsive instability remains unchanged under pressure for CaTiO3 and appears above 5 GPa for SrTiO3. Moreover, it is shown that at room pressure SrTiO3 was locally ferroelectric. A new phase appears for SrTiO3 above 14 GPa with a strong deformation of the oxygen octahedron.
TL;DR: In this article, a nonlinear constitutive materials model was developed and tested by means of advanced FEM calculations, which accounts for the pressure enhancement of elastic moduli and of flow stress.
Abstract: Recent progress in the understanding of the origin of hardness enhancement in superhard nc-TiN/a-Si3N4 nanocomposites (‘nc-’ stands for ‘nanocrystalline’, ‘a-’ for ‘X-Ray amorphous’) is summarized. The optimum nanostructure with one monolayer of interfacial Si 3N 4 was confirmed by both experiments with the deposition of TiN/Si3N4 heterostructures by Soderberg et al. and by first principle density functional theory calculations of Hao et al. These calculations show that the decohe-sion energy of the TiN/Si 3N 4/TiN sandwich is enhanced as compared with bulk Si 3N 4. A new, non-linear constitutive materials model, which accounts for the pressure enhancement of elastic moduli and of flow stress has been developed and tested by means of advanced FEM calculations. Significant deviation of the mechanical behaviour of super- and ultrahard materials from the prediction of linear mechanics with a constant yield stress has been demonstrated.