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The compression of argon is measured between 10 K and 296 K up to 20 GPa and and up to 114 GPa at 296 K in diamond anvil cells. Three samples conditioning are used: (1) single crystal sample directly compressed between the anvils, (2) powder sample directly compressed between the anvils, (3) single crystal sample compressed in a pressure medium. A partial transformation of the face-centered cubic (fcc) phase to a hexagonal close-packed (hcp) structure is observed above 4.2–13 GPa. Hcp phase forms through stacking faults in fcc-Ar and its amount depends on pressurizing conditions and starting fcc-Ar microstructure. The quasi-hydrostatic equation of state of the fcc phase is well described by a quasi-harmonic Mie–Grüneisen–Debye formalism, with the following 0 K parameters for Rydberg-Vinet equation: $$V_0$$ V 0 = 38.0 Å$$^3$$ 3 /at, $$K_0$$ K 0 = 2.65 GPa, $$K'_0$$ K 0 ′ = 7.423. Under the current experimental conditions, non-hydrostaticity affects measured P–V points mostly at moderate pressure ($$\le$$ ≤ 20 GPa).

The insertion of oxygen and nitrogen molecules in the one-dimensional (1D) pore system of the zeolite TON was studied at high pressure by vibrational spectroscopy, X-ray diffraction, and Monte Carlo (MC) molecular modeling. Rietveld refinements and MC modeling indicate that, on average, six diatomic molecules per unit cell enter the pores of the zeolite. This induces changes in compressibility and distortion related to the Cmc21-to-Pbn21 phase transition compared to the empty-pore material. The filling behavior with N2 and O2 under pressure is similar to that of argon, suggesting that the kinetic diameter, which is very close in these three systems, plays a major role. The orientation of the diatomic molecules appears to have a rather minor effect on filling occurring at a slightly higher pressure for N2, which has a larger kinetic diameter. Both inserted molecules, initially not showing any marked orientation, begin to exhibit a degree of orientational order above 2 GPa.

Physical review / B 103(13), 134103 (2021). doi:10.1103/PhysRevB.103.134103, Vanadium is reported to undergo a pressure-induced bcc-rhombohedral phase transition at 30–70 GPa, with a transition pressure that is sensitive to the hydrostaticity of the sample environment. However, the experimental evidence for the structure of the high-pressure phase being rhombohedral is surprisingly weak. We have restudied vanadium under pressure to 154 GPa using both polycrystalline and single-crystal samples, and a variety of different pressure transmitting media (PTM). We find that only when using single-crystal samples does one observe a rhombohedral high-pressure phase; the high-pressure diffraction profiles from the polycrystalline samples do not fit a rhombohedral lattice, irrespective of the PTM used. The single-crystal samples reveal two rhombohedral phases, with a continuous transition between them, and distortions from cubic symmetry are much smaller than previously calculated., Published by Inst., Woodbury, NY

Herein we show that ${\mathrm{Mo}}_{4}{\mathrm{Ce}}_{4}{\mathrm{Al}}_{7}{\mathrm{C}}_{3}$, a recently discovered nanolamellar compound displaying mixed valence, combines Kondo lattice behavior with ferromagnetism. A sizeable magnetization is carried by $3p$ states of Al as evidenced by a strong x-ray magnetic circular dichroism signal at the $K$ edge of aluminum, whereas no detectable signal was observed at the $K$ edge of carbon and ${L}_{2,3}$ edges of molybdenum. These results point out that the ferromagnetic behavior originates in the Ce atoms with $4{f}^{1}$ electronic configuration lying within the Al planes. The evolution with pressure of the mixed valence of Ce atoms in the Mo-C planes determined via Ce ${L}_{3}$ x-ray-absorption spectra along with the magnetoresistance measurements across the ferromagnetic transition unambiguously reveal a Kondo behavior. Angle-resolved photoemission spectroscopy and density functional theory confirm a certain degree of Ce $4f$ electron delocalization. More generally, conduction electrons are not restricted to lie in the MoC planes but are also delocalized in the Al planes.

International audience; The liquid-liquid transition (LLT), in which a single-component liquid transforms into another one via a first-order phase transition, is an intriguing phenomenon that has changed our perception of the liquid state. LLTs have been predicted from computer simulations of water 1,2 , silicon 3 , carbon dioxide 4 , carbon 5 , hydrogen 6 and nitrogen 7. Experimental evidence has been found mostly in supercooled (that is, metastable) liquids such as Y 2 O 3-Al 2 O 3 mixtures 8 , water 9 and other molecular liquids 10-12. However, the LLT in supercooled liquids often occurs simultaneously with crystallization, making it difficult to separate the two phenomena 13. A liquid-liquid critical point (LLCP), similar to the gas-liquid critical point, has been predicted at the end of the LLT line that separates the low-and high-density liquids in some cases, but has not yet been experimentally observed for any materials. This putative LLCP has been invoked to explain the thermodynamic anomalies of water 1. Here we report combined in situ density, X-ray diffraction and Raman scattering measurements that provide direct evidence for a first-order LLT and an LLCP in sulfur. The transformation manifests itself as a sharp density jump between the low-and high-density liquids and by distinct features in the pair distribution function. We observe a non-monotonic variation of the density jump with increasing temperature: it first increases and then decreases when moving away from the critical point. This behaviour is linked to the competing effects of density and entropy in driving the transition. The existence of a first-order LLT and a critical point in sulfur could provide insight into the anomalous behaviour of important liquids such as water.

We present a study on the phase stability of dense carbon dioxide (${\mathrm{CO}}_{2}$) at extreme pressure-temperature conditions, up to 6200 K within the pressure range $37\ifmmode\pm\else\textpm\fi{}9$ to $106\ifmmode\pm\else\textpm\fi{}17\text{ }\text{ }\mathrm{GPa}$. The investigations of high-pressure high-temperature in situ x-ray diffraction patterns recorded from laser-heated ${\mathrm{CO}}_{2}$, as densified in diamond-anvil cells, consistently reproduced the exclusive formation of polymeric tetragonal ${\mathrm{CO}}_{2}$-V at any condition achieved in repetitive laser-heating cycles. Using well-considered experimental arrangements, which prevent reactions with metal components of the pressure cells, annealing through laser heating was extended individually up to approximately 40 min per cycle in order to keep track of upcoming instabilities and changes with time. The results clearly exclude any decomposition of ${\mathrm{CO}}_{2}$-V into the elements as previously suggested. Alterations of the Bragg peak distribution on Debye-Scherrer rings indicate grain coarsening at temperatures $g4000\text{ }\text{ }\mathrm{K}$, giving a glimpse of the possible extension of the stability of the polymeric solid phase.

The phase diagram and melting curve of water ice is investigated up to 45 GPa and 1600 K by synchrotron x-ray diffraction in the resistively and laser heated diamond anvil cell. Our melting data evidence a triple point at 14.6 GPa, 850 K. The latter is shown to be related to a first-order solid transition from the dynamically disordered form of ice VII, denoted ice ${\mathrm{VII}}^{\ensuremath{'}}$, toward a high-temperature phase with the same bcc oxygen lattice but larger volume and higher entropy. Our experiments are compared to ab initio molecular dynamics simulations, enabling us to identify the high-temperature bcc phase with the predicted superionic ice ${\mathrm{VII}}^{\ensuremath{'}\ensuremath{'}}$ phase [J.-A. Hernandez and R. Caracas, Phys. Rev. Lett. 117, 135503 (2016).].

Electron-phonon interaction is of central importance for the electrical and heat transport properties of metals, and is directly responsible for charge-density-waves or (conventional) superconducting instabilities. The direct observation of phonon dispersion anomalies across electronic phase transitions can provide insightful information regarding the mechanisms underlying their formation. Here, we review the current status of phonon dispersion studies in superconductors under hydrostatic and uniaxial pressure. Advances in the instrumentation of high resolution inelastic X-ray scattering beamlines and pressure generating devices allow these measurements to be performed routinely at synchrotron beamlines worldwide., 8 pages, 6 figures. Invited review submitted to Superconductor Science and Technology, Focus issue on Hydride & High-Pressure Superconductors. References in figure caption fixed. Hyperlinks added

International audience; Properties of liquid silicates under high pressure and high temperature conditions are critical for modeling the dynamics and solidification mechanisms of the magma ocean in the early Earth, as well as for constraining entrainment of melts in the mantle and in the present-day core-mantle boundary. Here, we present in situ structural measurements by X-ray diffraction of selected amorphous silicates compressed statically in diamond anvil cells (up to 157 GPa at room temperature) or dynamically by laser-generated shock compression (up to 130 GPa and 6000 K along the MgSiO3 glass Hugoniot). The X-ray diffraction patterns of silicate glasses and liquids reveal similar characteristics over a wide pressure and temperature range. Beyond the increase in Si coordination observed at 20 GPa, we find no evidence for major structural changes occurring in the silicate melts studied up to pressures and temperatures exceeding Earth's core mantle boundary conditions. This result is supported by molecular dynamics calculations. Our findings reinforce the widely-used assumption that the silicate glasses studies are appropriate structural analogs for understanding the atomic arrangement of silicate liquids at these high pressures.

Single crystals of solid chlorine (Cl2) were synthesized at room temperature and high pressure (HP, P=1.45 GPa) in a diamond anvil cell (DAC). At these conditions Cl2 adapts the same structure as its corresponding low-temperature (LT) ambient pressure modification (TCmce spacegroup) with Cl2 molecules forming monolayers parallel to the bc plane and this structure is preserved up to at least 64 GPa. The pressure of 1.45 GPa is to be considered as a solidification point of liquid Cl2 at room temperature.

Iron oxides are among the major constituents of the deep Earth’s interior. Among them, the epsilon phase of Fe2O3 is one of the less studied polymorphs and there is a lack of information about its structural, electronic and magnetic transformations at extreme conditions. Here we report the precise determination of its equation of state and a deep analysis of the evolution of the polyhedral units under compression, thanks to the agreement between our experiments and ab-initio simulations. Our results indicate that this material, with remarkable magnetic properties, is stable at pressures up to 27 GPa. Above 27 GPa, a volume collapse has been observed and ascribed to a change of the local environment of the tetrahedrally coordinated iron towards an octahedral coordination, finding evidence for a different iron oxide polymorph., Iron oxides exist in a variety of polymorphs at different pressure and temperature conditions, displaying important magnetic properties, and are major constituents of the Earth’s interior. Here the authors investigate the structural and electronic changes in the uncommon epsilon phase under compression to deep Mantle pressures.

In this article we present a direct comparison between reflective (Schwarzschild mirrors) and refractive (achromatic doublets) optics commonly used in spectroradiometric temperature measurements in...

Rb0.5Cs2.5C60 is a member of the family of face-centred-cubic (fcc)–structured alkali fullerides, A3C60 (A = alkali metal) with a highly expanded lattice size. At ambient temperature and pressure, it is a Mott–Jahn–Teller insulator. However, upon cooling it exhibits first a crossover to an anomalous metallic state (Jahn–Teller metal) in the vicinity of 90 K followed next by a transition to a bulk superconductor with a transition temperature, Tc of 29.4 K. Here we study its structural and electronic response to the application of pressure. Synchrotron X-ray powder diffraction at ambient temperature shows that the same Mott-insulator–metal electronic state crossover can be induced through pressure application under isothermal conditions, as evidenced by a distinct broad symmetry-preserving compressibility anomaly, which sets in at ∼0.4 GPa and extends to ∼0.75 GPa. Complementary magnetic susceptibility measurements also reveal that the crossover temperature, T′ tunable at ambient pressure through adjusting the dopant ratio to vary the unit cell volume, can be controlled through pressure application and be mapped onto the same global electronic phase diagram. The observed electronic response, as a function of both physical and ‘chemical’ pressure, is thus of the same electronic origin, namely the control of the bandwidth, W via outer wave function overlap of the constituent fulleride ions.

A review of some important technical challenges related to in situ diamond anvil cell laser heating experimentation at synchrotron X-ray sources is presented. The problem of potential chemical reactions between the sample and the pressure medium or the carbon from the diamond anvils is illustrated in the case of elemental tantalum. Preliminary results of a comparison between reflective and refractive optics for high temperature measurements in the laser-heated diamond anvil cell are briefly discussed. Finally, the importance of the size and relative alignment of X-ray and laser beams for quantitative X-ray measurements is presented.

Co-auteur étranger; International audience; The structure of liquid silicates is commonly described as a statistical mixture of various atomic entities with relative abundances that can vary with pressure, temperature and composition. Unfortunately, this view remains largely theoretical due to scarce experimental reports on the silicate melt structure, in particular under pressure. We performed X-ray diffraction of the SiO2 end-member to probe the melting curve up to ~120 GPa and 7000 K, and the melt structure up to ~80 GPa. We confirm the steep increase of the melting curve above ~14 GPa when stishovite becomes stable over coesite in subsolidus conditions, with a slope of about 80 K/GPa. Then, around 45 GPa and 5400 K, the melting curve flattens significantly, an effect most likely reflecting the densification of the SiO2 melt structure. The signal of diffuse X-ray scattering is compatible with a change of the Si coordination number from 4 to 6 along the melting curve, in agreement with previous works reporting a similar evolution during the cold compression of SiO2-glass. Because of the limited pressure range (within 10 to 20 GPa) in which the melting curve changes its slope, we speculate a difficult coexistence of tetrahedral SiO4 and octahedral SiO6 units in SiO2 melt at high pressures.

At ambient pressure the spinel $\mathrm{Li}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ is a metal with a heavy fermion ground state. However, under applied pressure a transition to an insulating, nonmagnetic state occurs. Powder x-ray diffraction has been used to study structural changes associated with this transition, and reveals that the ambient-pressure $Fd\overline{3}m$ spinel structure distorts to a monoclinic cell of $C2/m,C2$, or $Cm$ symmetry above 11 GPa at low temperatures. The changes of structure and properties provide evidence for orbital molecule formation in the cubic phase at high pressures and low temperatures that leads to long-range orbital molecule order in the monoclinic phase.

International audience; The melting curve of gold has been measured up to 110 GPa using laser-heated diamond anvil cells and synchrotron x-ray diffraction techniques. Accurate pyrometry temperature measurements and a homogeneous heating of the gold sample were achieved by implementing a sample assembly consisting of two boron-doped diamond cupped disks sandwiching the gold sample. In the investigated pressure range, the fcc solid gold remains stable up to melting. A clear structural signature of bulk melting is observed. Ab initio molecular dynamics simulations within the two-phase approach give a melting curve in good agreement with the experimental one. We discuss the validity of calculations based on the Lindemann criteria of melting which have been up to now used to obtain the melting line of Au in the 100 GPa range.

The structure of liquid ammonia (${\mathrm{NH}}_{3}$) is investigated from 1 to 6.3 GPa and up to 800 K by means of synchrotron x-ray diffraction (XRD) and ab initio molecular dynamics (AIMD) simulations. The XRD data are used to extract the molecular structure factor ${S}_{\mathrm{mol}}(Q)$, pair distribution function (PDF) ${g}_{\mathrm{mol}}(r)$, and the density of ${\mathrm{NH}}_{3}$. There is an excellent agreement between present ${S}_{\mathrm{mol}}(Q)$ and ${g}_{\mathrm{mol}}(r)$ at our lowest density and those reported in reference neutron experiments. Our densities agree better with the equation of state (EoS) of Tillner-Roth et al. [DKV-Tagungsbericht (Hannover, New York, 1993), Vol. 20, p. 167] than with more recent EoS models. The experimental structure factor and PDF are well reproduced by AIMD simulations using either the Becke-Lee-Yang-Parr or the Perdew-Burke-Ernzerhof exchange-correlation functional. The shapes of ${S}_{\mathrm{mol}}(Q)$ and ${g}_{\mathrm{mol}}(r)$ vary little over the investigated pressure range and suggest a compact liquid with weak orientational correlations between molecules, which is corroborated by the coordination number varying from 12.7 to $\ensuremath{\sim}14$. The simulations are used to study the evolution of the site-site pair distribution functions, which reveals that the number of H bonds per molecule (between 1.5 and 2) do not evolve with density and that the distribution of H atoms around N atoms becomes more and more anisotropic with pressure.

Melting experiments require rapid data acquisition due to instabilities of the molten sample and optical drifting due to the high required laser power. In this work, the melting curve of zirconium has been determined for the first time up to 80 GPa and 4000 K using in-situ fast x-ray diffraction (XRD) in a laser-heated diamond anvil cell (LH-DAC). The main method used for melt detection was the direct observance of liquid diffuse scattering (LDS) in the XRD patterns and it has been proven to be a reliable melting diagnostic. The effectiveness of other melting criteria such as the appearance temperature plateaus with increasing laser power is also discussed.

Xe–Ni and Xe–Fe systems are studied in a pressure range relevant to the Earth's core (135–210 GPa) using laser-heated diamond anvil cells and synchrotron X-ray diffraction. The stability of several intermetallic compounds, including XeNi3 and XeFe3, has been recently calculated using structural searches and density functional theory (DFT) above 155 and 190 GPa, respectively [Zhu L, Liu H, Pickard CJ, et al. Nat Chem. 2014;6:644–648]. We have synthesized XeNi3 around 150 GPa, confirming the prediction; however, it has a cubic Pm3¯m-Cu3Au structure, different from the predicted one for XeNi3 but identical to the structure predicted for XeFe3. Pm3¯m-XeNi3 is calculated to be metastable with DFT. A disordered Ni1−xXex (x∼0.08) alloy is observed to form prior to this compound. This alloy is interesting in the perspective of a possible storage of xenon in the Earth's core. We have not observed any reaction between Xe and Fe up to 210 GPa.

New insight into the superconducting properties of HgBa2CuO4 (Hg-1201) cuprates is provided by combined measurements of electrical resistivity and single crystal X-ray diffraction under pressure. The changes induced by increasing pressure up to 20 GPa in optimally doped single crystals were investigated. The resistivity measurements as a function of temperature show a metallic behavior up to ~10 GPa that gradually passes into an insulating state, typical of charge ordering, which totally suppresses superconductivity above 13 GPa. The changes in resistivity are accompanied by the apparition of sharp Bragg peaks in the X-ray diffraction patterns, indicating that the charge ordering is accompanied by a 3D oxygen ordering. Considering that pressure induces a charge transfer of about 0.02 at 10 GPa, our results are the first observation of charge order competing with superconductivity developed in the overdoped region of the phase diagram of a Hg-based cuprate.

BaFe2Se3 is a potential superconductor material exhibiting transition at 11 K and ambient pressure. Here we extended the structural and performed electrical resistivity measurements on this compound up to 51 GPa and 20 GPa, respectively, in order to distinguish if the superconductivity in this sample is intrinsic to the BaFe2Se3 phase or if it is originating from minor FeSe impurities that show a similar superconductive transition temperature. The electrical resistance measurements as a function of pressure show that at 5 GPa the superconducting transition is observed at around 10 K, similar to the one previously observed for this sample at ambient pressure. This indicates that the superconductivity in this sample is intrinsic to the BaFe2Se3 phase and not to FeSe with Tc > 20 K at these pressures. Further increase in pressure suppressed the superconductive signal and the sample remained in an insulating state up to the maximum achieved pressure of 20 GPa. Single-crystal and powder X-ray diffraction measurements revealed two structural transformations in BaFe2Se3: a second order transition above 3.5 GPa from Pnma (CsAg2I3-type structure) to Cmcm (CsCu2Cl3-type structure) and a first order transformation at 16.6 GPa. Here, {\gamma}-BaFe2Se3 transforms into {\delta}-BaFe2Se3 (Cmcm, CsCu2Cl3-type average structure) via a first order phase transition mechanism. This transitions is characterized by a significant shortening of the b lattice parameter of {\gamma}-BaFe2Se3 (17%) and accompanied by an anisotropic expansion in the orthogonal ac plane at the transition point.

This work reports on the pressure dependence of the octahedral tilts and mean Fe-O bond lengths in $R\mathrm{Fe}{\mathrm{O}}_{3}$ ($R=\mathrm{Nd}$, Sm, Eu, Gd, Tb, and Dy), determined through synchrotron x-ray diffraction and Raman scattering, and their role on the pressure-induced phase transition displayed by all of these compounds. For larger rare-earth cations (Nd-Sm), both anti- and in-phase octahedral tilting decrease as pressure increases, whereas the reverse behavior is observed for smaller ones (Gd-Dy). $\mathrm{EuFe}{\mathrm{O}}_{3}$ stands at the borderline, with nearly pressure-independent tilt angles. For the compounds where the tilts increase with pressure, the $\mathrm{Fe}{\mathrm{O}}_{6}$ octahedra are compressed at lower rates than for those ones exhibiting opposite pressure tilt dependence. The crossover between the two opposite pressure behaviors is discussed in relation to the general rules proposed from different theoretical approaches. The similarity of the pressure-induced isostructural insulator-to-metal phase transition, observed in the whole series, points out that the tilts play a minor role in its driving mechanisms. A clear relationship between octahedral compressibility and critical pressure is ascertained.

The melting curve and stability of ammonia (${\mathrm{NH}}_{3}$) is investigated up to 40 GPa and 3500 K by x-ray diffraction and Raman spectroscopy in the laser-heated diamond anvil cell. The ${\mathrm{NH}}_{3}$ samples were directly heated by the $10.6\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$ radiation of a ${\mathrm{CO}}_{2}$ laser to reduce the risks of chemical reactions. Melting was unambiguously detected by the appearance of the liquid diffraction signal upon temperature increase. The melting temperature of ${\mathrm{NH}}_{3}$ is found to steadily increase with pressure up to 40 GPa, and the previously reported turnover is not observed. As a result, the melting line of ${\mathrm{NH}}_{3}$ is expected to cross the isentropes of Neptune and Uranus in the pressure range 55--65 GPa, implying the possible presence of superionic solid ${\mathrm{NH}}_{3}$ in these planets. Our x-ray and Raman measurements confirm the appearance of ${\mathrm{N}}_{2}$ and ${\mathrm{H}}_{2}$ upon heating the liquid phase from 6 to 40 GPa. But while the equilibrium $2{\mathrm{NH}}_{3}\ensuremath{\rightleftharpoons}{\mathrm{N}}_{2}+3{\mathrm{H}}_{2}$ balances towards the dissociated elements at low pressure and high temperature, ammonia is found to the more stable species in the range 20--40 GPa, 300--3000 K.

Cuprates exhibit antiferromagnetic, charge density wave (CDW), and high-temperature superconducting ground states that can be tuned by means of doping and external magnetic fields. However, disorder generated by these tuning methods complicates the interpretation of such experiments. Here, we report a high-resolution inelastic x-ray scattering study of the high-temperature superconductor YBa₂Cu₃O6.67 under uniaxial stress, and we show that a three-dimensional long-range-ordered CDW state can be induced through pressure along the a axis, in the absence of magnetic fields. A pronounced softening of an optical phonon mode is associated with the CDW transition. The amplitude of the CDW is suppressed below the superconducting transition temperature, indicating competition with superconductivity. The results provide insights into the normal-state properties of cuprates and illustrate the potential of uniaxial-pressure control of competing orders in quantum materials., Facultad de Ciencias Exactas, Instituto de Física de Líquidos y Sistemas Biológicos

Carbon dioxide is a widespread simple molecule in the Universe. In spite of its simplicity it has a very complex phase diagram, forming both amorphous and crystalline extended phases above 40 GPa. The stability range and nature of these phases are still debated, especially in view of their possible role within the deep carbon cycle. Here, we report static synchrotron X-ray diffraction and Raman high-pressure experiments in the megabar range providing evidence for the stability of the polymeric phase V at pressure-temperature conditions relevant to the Earth’s lowermost mantle. The equation of state has been extended to 120 GPa and, contrary to earlier experimental findings, neither dissociation into diamond and ε-oxygen nor ionization was observed. Severe deviatoric stress and lattice deformation along with preferred orientation are removed on progressive annealing, thus suggesting CO2-V as the stable structure also above one megabar., The nature and stability of carbon dioxide under extreme conditions relevant to the Earth’s mantle is still under debate, in view of its possible role within the deep carbon cycle. Here, the authors perform high-pressure experiments providing evidence that polymeric crystalline CO2 is stable under megabaric conditions.

We investigated the atomic structure of liquid Rb along an isothermal path at 573 K, up to 23 GPa, by X-ray diffraction measurements. By raising the pressure, we observed a liquid–liquid transformation from a simple metallic liquid to a complex one. The transition occurs at 7.5 ± 1 GPa which is slightly above the first maximum of the T–P melting line. This transformation is traced back to the density-induced hybridization of highest electronic orbitals leading to the accumulation of valence electrons between Rb atoms and to the formation of interstitial atomic shells, a behavior that Rb shares with Cs and is likely to be common to all alkali metals.

We present the pressure-temperature phase diagram of the antiferromagnet CeAg2Si2 established via resistivity and calorimetry measurements under quasi-hydrostatic conditions up to 22.5 GPa. With increasing pressure, the Neel temperature [ T N ( p = 0 ) = 8.6 K] slowly increases up to T N = 13.4 K at 9.4 GPa and then vanishes abruptly at the magnetic critical pressure p c ∼ 13 GPa. For the first time, heavy fermion superconductivity is observed in CeAg2Si2. Superconductivity emerges at ∼ 11 GPa and persists over roughly 10 GPa. Partial- and bulk-transition temperatures are highest at p = 16 GPa, with a maximal T c bulk = 1.25 K. In the pressure region of superconductivity, Kondo and crystal-field splitting energies become comparable and resistivity exhibits clear signatures of a Ce-ion valence crossover. The crossover line is located at a rapid collapse in resistivity as function of pressure and extrapolates to a valence transition critical endpoint at critical pressure and temperature of p cr ∼ 17 GPa and T cr ∼ − 13 K , respectively. Both critical spin and valence fluctuations may build up superconductivity in CeAg2Si2.

Solid krypton (Kr) undergoes a pressure-induced martensitic phase transition from a face-centered cubic (fcc) to a hexagonal close-packed (hcp) structure. These two phases coexist in a very wide pressure domain inducing important modifications of the bulk properties of the resulting mixed phase system. Here, we report a detailed in situ x-ray diffraction and absorption study of the influence of the fcc-hcp phase transition on the compression behavior of solid krypton in an extended pressure domain up to 140 GPa. The onset of the hcp-fcc transformation was observed in this study at around 2.7 GPa and the coexistence of these two phases up to 140 GPa, themaximum investigated pressure. The appearance of the hcp phase is also evidenced by the pressure-induced broadening and splitting of the first peak in the XANES spectra. We demonstrate that the transition is driven by a continuous nucleation and intergrowth of nanometric hcp stacking faults that evolve in the fcc phase. These hcp stacking faults are unaffected by high-temperature annealing, suggesting that plastic deformation is not at their origin. The apparent small Gibbs free-energy differences between the two structures that decrease upon compression may explain the nucleation of hcp stacking faults and the large coexistence domain of fcc and hcp krypton. We observe a clear anomaly in the equation of state of the fcc solid at ∼20 GPa when the proportion of the hcp form reaches ∼20%.We demonstrate that this anomaly is related to the difference in stiffness between the fcc and hcp phases and propose two distinct equation of states for the low and high-pressure regimes.

We report on the effects of hydrostatic pressure (HP) on the charge density wave observed in underdoped cuprates. We studied ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.6}\phantom{\rule{4pt}{0ex}}({T}_{c}=61$ K) using high-resolution inelastic x-ray scattering (IXS), and reveal an extreme sensitivity of the phonon anomalies related to the charge density wave (CDW) order to HP. The amplitudes of the normal state broadening and superconductivity-induced phonon softening at ${\mathbf{Q}}_{\text{CDW}}$ rapidly decrease as HP is applied, resulting in the complete suppression of signatures of the CDW below $\ensuremath{\sim}10$ kbar. Additional IXS measurements on ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.75}$ demonstrate that this very rapid effect cannot be explained by pressure-induced modification of the doping level and highlight the different role of external pressure and doping in tuning the phase diagram of the cuprates. Our results provide insights into the mechanisms underlying the CDW formation and its interplay with superconductivity.

International audience; The high-pressure behavior of LuFe2O4 is characterized based on synchrotron X-ray diffraction and neutron diffraction, resistivity measurements, X-ray absorption spectroscopy and infrared spectroscopy studies. The results obtained enabled us to propose a P-T phase diagram. In this study, the low pressure charge-ordering melting could be detected by synchrotron XRD in the P-T space. In addition to the ambient pressure monoclinic C2/m and rhombohedral R(3) over bar m phases, the possible P (1) over bar triclinic phase, the monoclinic high pressure form Pm and metastable modulated monoclinic phases were observed; the latter modulated monoclinic phases were not observed in the present neutron diffraction data. Furthermore, the transition to the Pm phase which was already characterized by strong kinetics is found to be favored at high temperature (373 K). Based on X-ray absorption spectroscopy data the Pm phase, which could be recovered at atmospheric pressure, can be explained by a change in the Fe-local environment from a five-fold coordination to a distorted 5 + 1 one.

International audience; Synchrotron x-ray diffraction measurements of nitrogen are performed up to 120 GPa to determine the melting curve and the structural changes of the solid and liquid phases along it. The melting temperature exhibits a monotonic increase up to the triple point where the epsilon molecular solid, the cubic gauche covalent solid, and the fluid meet at 116 GPa, 2080 K. Above, the stability of the cubic gauche phase induces a sharp increase of the melting curve. The structural data on liquid nitrogen show that the latter remains molecular over the whole probed domain, which contradicts the prediction of a liquid-liquid transition at 88 GPa, 2000 K. These findings thus largely revisit the phase diagram of hot dense nitrogen and challenge the current understanding of this model system.

Magnetic, electronic, and structural properties of $M\mathrm{F}{\mathrm{e}}_{2}{\mathrm{O}}_{4} (M=\mathrm{Mg},\mathrm{Zn},\mathrm{Fe})$ ferric spinels have been studied by $^{57}\mathrm{Fe}$ M\"ossbauer spectroscopy, electrical conductivity, and powder and single-crystal x-ray diffraction (XRD) to a pressure of 120 GPa and in the 2.4--300 K temperature range. These studies reveal for all materials, at the pressure range 25--40 GPa, an irreversible first-order structural transition to the postspinel $\mathrm{CaT}{\mathrm{i}}_{2}{\mathrm{O}}_{4}\ensuremath{-}$ type structure (Bbmm) in which the HS $\mathrm{F}{\mathrm{e}}^{3+}$ occupies two different crystallographic sites characterized by six- and eightfold coordination polyhedra, respectively. Above 40 GPa, an onset of a sluggish second-order high-to-low spin (HS-LS) transition is observed on the octahedral $\mathrm{F}{\mathrm{e}}^{3+}$ sites while $\mathrm{F}{\mathrm{e}}^{3+}$ occupying bicapped trigonal prism sites remain in the HS state. Despite an appreciable resistance decrease, corroborating with the transition to the LS state, $\mathrm{MgF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ and $\mathrm{ZnF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ remain semiconductors at this pressure range. However, in the case of $\mathrm{F}{\mathrm{e}}_{3}{\mathrm{O}}_{4}$, the second-order HS-LS transition on the $\mathrm{F}{\mathrm{e}}^{3+}$ octahedral sites corroborates with a clear trend to a gap closure and formation of a semimetal state above 50 GPa. Above 65 GPa, another structural phase transition is observed in $\mathrm{F}{\mathrm{e}}_{3}{\mathrm{O}}_{4}$ to a new Pmma structure. This transition coincides with the onset of nonmagnetic $\mathrm{F}{\mathrm{e}}^{2+}$, signifying further propagation of the gradual collapse of magnetism corroborating with a sluggish metallization process. With this, half of $\mathrm{F}{\mathrm{e}}^{3+}$ sites remain in the HS state. Thus, this paper demonstrates that, in a material with a complex crystal structure containing transition metal cation(s) in different environments, a HS-LS transition and delocalization/metallization of the $3d$ electrons does not necessarily occur simultaneously and may propagate through different crystallographic sites at different degrees of compression.

We report the synthesis and characterization of the novel silicide LaFeSiH displaying superconductivity with onset at 11 K. We find that this pnictogen-free compound is isostructural to LaFeAsO, with a similar low-temperature tetragonal to orthorhombic distortion. Using density functional theory we show that this system is also a multiband metal in which the orthorhombic distortion is likely related to single-stripe antiferromagnetic order. Electrical resistivity and magnetic susceptibility measurements reveal that these features occur side-by-side with superconductivity, which is suppressed by external pressure., Comment: 5 + epsilon pages, 7 figures, Supplemental Material on demand; v2 includes additional magnetization and resistivity data; v3 includes additional resistivity data from LaFeSiH single crystal

International audience; We have developed an experimental setup at the ESRF beamline ID12 dedicated to X-ray absorption and magnetic circular dichroism measurements at high pressure adapted for the tender X-ray energy range and compatible with low temperatures and with high magnetic field. The focused incoming X-ray beam passes through a thin diamond disk attached to a fully perforated diamond anvil and X-ray fluorescence photons from the sample are collected in back-scattering geometry through the same diamond disk. The pressure in the cell is measured using the ruby luminescence through a full diamond anvil. The highest pressure attainable with this diamond anvil cell (DAC) depends on the thickness of the diamond disk and it is above 16 GPa for a 80-μm thick plate and exceeds 4.5 GPa in the case of 30-μm diamond disk. Excellent performances of this setup in the tender X-ray range are illustrated with X-ray absorption near-edge structure studies of the phase transitions in KCl at the potassium and chlorine K-edges (3.61 and 2.82 keV, respectively) as well as in CdS at the sulfur K-edge (2.47 keV). This DAC together with a dedicated total fluorescence yield (TFY) detector could be mounted in the main heat exchanger of a cryostat and inserted in a bore of a superconducting magnet, this makes possible to perform X-ray magnetic circular dichroism (XMCD) experiments at low temperature, high magnetic field and high pressure. Feasibility of this approach is shown with the XMCD results obtained at the U M4,5-edges in ferromagnetic superconductor UGe2.

The material ZrTe3 is a well-known example of an incommensurate periodic lattice distortion (PLD) at low temperatures due to a charge density wave (CDW). Previous studies have found a sharp boundary as a function of pressure between CDW below 5 GPa and bulk superconductivity above this value. We present a study of low-temperature-high-pressure single crystal x-ray diffraction along with ab initio density functional theory calculations. The modulation vector q(CDW) is found to change smoothly with pressure until the PLD is lost. Fermi surface calculations reproduce these changes, but neither these nor the experimental crystal lattice structure show a particular step change at 5 GPa, thus leading to the conclusion that the CDW is lost accidentally by tipping the balance of CDW formation in the Fermi surface nesting that stabilizes it.

International audience; Highly perfect single crystal whiskers of Lu5Ir4Si10 were successfully grown out of the melt. Details of the surface and morphology of the whiskers are presented. X-ray diffraction data confirmed that the whisker structure has the same tetragonal P4/mbm space group symmetry as bulk single crystals with lattice parameters a=12.484(1) and c=4.190(2) Å. By means of field emission scanning electron microscopy, the morphology of the whiskers has been studied. Using a 4-circle X-ray diffractometer we found that whiskers grow along the c-axis direction and all side faces are oriented along the [1 1 0] direction. The mosaicity has been measured and is found to be almost perfect: below 0.15° along the c-axis. According to our transport measurements performed along the c-axis, the whiskers present a sharp superconducting transition at Tc=4.1 K and show a charge density wave (CDW) transition at 77 K. From the hysteresis of the temperature dependance of the electrical resistivity study, the CDW transition is found to be of first order.

The magnetic and structural properties of cobalt were investigated under high pressure (160 GPa) and low temperature (50 K), by synchrotron K-edge x-ray magnetic circular dichroism and x-ray diffraction. A quasihydrostatic equation of state was measured up to 160 GPa. We found that uniaxial stress plays a role in the hexagonal close packed-face centered cubic (hcp-fcc) structural transition pressure. Also, our data provide the first experimental evidence that changes of the $c/a$ ratio pressure derivative are related to the magnetic behavior. The complete extinction of ferromagnetism is observed above 130 GPa in a mixed hcp-fcc phase with no recovery upon cooling to 50 K, indicating that cobalt at 150 GPa is very likely nonmagnetic, i.e., characterized by zero local spin polarization. Density functional theory calculations point out that the K-edge x-ray magnetic circular dichroism (XMCD) signal is related to the $4p$ orbital moment rather than to the total spin moment and allow us to get a deeper insight into the K-edge XMCD measurements interpretation. The combination of novel theoretical results and experimental outputs provides a detailed scenario of the structural and magnetic properties of cobalt at these extreme conditions answering some previously unsolved issues.

The diamond anvil cell (DAC) is a fundamental device used to explore the properties of materials under extreme pressure and temperature (P/T) conditions. In the past years, simultaneous high P/T DAC experiments using the resistively heated DAC (RH-DAC) techniques have been developed for studying materials properties in a wide P/T range. However, the mechanical instability of metallic gaskets used for sample confinement at high P/T conditions remains a limiting factor for exploiting the accessible P/T range of the RH-DAC. In this study, we present a new gasket configuration that overcomes these limitations. It is based on an amorphous boron–epoxy mixture inserted in a rhenium gasket. We show how these gasket inserts stabilize the sample chamber over a wide P/T range, allowing monitoring sample properties using X-ray diffraction and absorption spectroscopy up to 50 GPa and 1620 K.

The interplay between charge density wave (CDW) order and superconductivity has attracted much attention. This is the central issue of a long standing debate in simple transition metal dichalcogenides without strong electronic correlations, such as 2H-NbSe$_2$, in which two such phases coexist. The importance of anisotropic electron-phonon interaction has been recently highlighted from both theoretical and experimental point of view, and explains some of the key features of the formation of the CDW in this system. On the other hand, other aspects, such as the effects of anharmonicity, remain poorly understood despite their manifest importance in such soft-phonon driven phase transition. At the theoretical level in particular, their prohibitive computational price usually prevents their investigation within conventional perturbative approaches. Here, we address this issue using a combination of high resolution inelastic X-ray scattering measurements of the phonon dispersion, as a function of temperature and pressure, with state of the art ab initio calculations. By explicitly taking into account anharmonic effects, we obtain an accurate, quantitative, description of the (P,T) dependence of the phonon spectrum, accounting for the rapid destruction of the CDW under pressure by zero mode vibrations - or quantum fluctuations - of the lattice. The low-energy longitudinal acoustic mode that drives the CDW transition barely contributes to superconductivity, explaining the insensitivity of the superconducting critical temperature to the CDW transition.

A superconductivity dome is created by the electronic structure of the molecular building block of an unconventional superconductor., Understanding the relationship between the superconducting, the neighboring insulating, and the normal metallic state above Tc is a major challenge for all unconventional superconductors. The molecular A3C60 fulleride superconductors have a parent antiferromagnetic insulator in common with the atom-based cuprates, but here, the C603– electronic structure controls the geometry and spin state of the structural building unit via the on-molecule Jahn-Teller effect. We identify the Jahn-Teller metal as a fluctuating microscopically heterogeneous coexistence of both localized Jahn-Teller–active and itinerant electrons that connects the insulating and superconducting states of fullerides. The balance between these molecular and extended lattice features of the electrons at the Fermi level gives a dome-shaped variation of Tc with interfulleride separation, demonstrating molecular electronic structure control of superconductivity.

The theoretical description of the electronic properties of iron under pressure involves the strong electronic correlations in this metal. We provide here reference structural data which can be used for this description. These data have been collected at low to ambient temperature in diamond anvil cells, under quasi-hydrostatic compression, using X-ray diffraction. The compression curves of α-Fe and ϵ-Fe have been measured up to 99.5 GPa along an isotherm at 15 K and the thermal expansion of ϵ-Fe has been measured between 15 K and 300 K at ∼57 GPa. The theoretical framework used in the literature which reproduces at best the compression curve of ϵ-Fe is dynamical mean field theory. The current measurements do not evidence any electronic topological transition in the scanned pressure range, where ϵ-Fe exhibits the behaviour of a Debye solid.

The structure and equation of state of the crystalline molecular phase II of carbon dioxide have been investigated at room temperature from 15.5 to 57.5 GPa using synchrotron x-ray diffraction methods. The CO${}_{2}$ samples were embedded in neon pressure medium in order to provide quasihydrostatic conditions. The x-ray diffraction patterns of phase II are best described by a tetragonal structure, with space group $P{4}_{2}/mnm$ and 2 molecules per unit cell, in accordance with a previous study [Yoo et al., Phys. Rev. B 65, 104103 (2002)]. There is however a large (15%) difference in the intramolecular C=O bond length between the present study, 1.14(3) \AA{}, and the latter work (1.329--1.366 \AA{}). The present value is similar to that of the free molecule and is in very good agreement with predictions based on density functional theory. The compressibility of CO${}_{2}$-II determined here also disagrees with the previous study: our value for the zero-pressure bulk modulus, ${B}_{0}=8.5(3)$ GPa [with ${B}_{0}^{\ensuremath{'}}={(\ensuremath{\partial}B/\ensuremath{\partial}P)}_{0}=6.29$], is 15.5 times smaller. These findings oppose the view that CO${}_{2}$-II is an intermediate state between the low-pressure molecular phases and the high-pressure nonmolecular forms, consistent with our previous results for phase IV [Datchi et al., Phys. Rev. Lett. 103, 185701 (2009)]. The x-ray diffraction patterns of CO${}_{2}$-II above 15 GPa indicate the presence of a large orthorhombic microstrain. Carrying out density functional theory calculations of the elastic tensor and stress-strain relation, we interpret this as due to the softness of the crystal against deviatoric stress in the [110] and symmetry-related directions. Unlike the other dioxides of the group-14 elements, there is however no mechanical or dynamical instability of the $P{4}_{2}/mnm$ structure in CO${}_{2}$ up to 57.5 GPa at 295 K, and therefore no symmetry lowering to $Pnnm$.

International audience; The Zn6Sc 1/1 cubic approximant to a quasicrystal has been studied in-situ at high pressures by single-crystal X-ray diffraction. This phase can be described as a bcc packing of Tsai-type icosahedral clusters whose center is occupied by a disordered Zn-4 tetrahedron. At ambient pressure the Zn6Sc undergoes a structural phase transition at 159 K to a monoclinic superstructure in which the Zn-4 tetrahedra are orientationally ordered along the [101] direction of the high-temperature bcc phase. In the pressure range up to 35 GPa, two new superstructures have been observed. The second phase corresponds to a four-fold pseudo cubic superstructure, i.e. a very large unit cell with a lattice parameter of about 5.5 nm. The resulting pressure-temperature phase diagram is different from that of Cd6Yb, which was reported by Watanuki et al. (2006).

We report experimental and theoretical evidence that solid molecular ammonia becomes unstable at room temperature and high pressures and transforms into an ionic crystalline form. This material has been characterized in both hydrogenated (NH${}_{3}$) and deuterated (ND${}_{3}$) ammonia samples up to about 180 and 200 GPa, respectively, by infrared absorption, Raman spectroscopy, and x-ray diffraction. The presence of a new strong infrared absorption band centered at 2500 cm${}^{\ensuremath{-}1}$ in NH${}_{3}$ (1900 cm${}^{\ensuremath{-}1}$ in ND${}_{3}$) is in line with previous theoretical predictions regarding the ionization of ammonia molecules into ${{\mathrm{NH}}_{2}}^{\ensuremath{-}}$ and ${{\mathrm{NH}}_{4}}^{+}$ ions. The experimental data suggest the coexistence of two crystalline ionic forms, which our ab initio structure searches predict to be the most stable at the relevant pressures. The ionic crystalline form of ammonia appears stable at low temperatures, which contrasts with the behavior of water in which no equivalent crystalline ionic phase has been found.

Recently, a golden colored, dense polymorph of titanium sesquioxide, Ti${}_{2}$O${}_{3}$ with a Th${}_{2}$S${}_{3}$-type structure, has been synthesized at high-pressure high-temperature conditions. In this paper, we present results of investigations of structural, optical, and electronic transport properties of this unusual golden polymorph of Ti${}_{2}$O${}_{3}$ under high pressure. Several experimental techniques were used, including x-ray diffraction studies using synchrotron radiation, Raman spectroscopy, electrical resistivity, and thermoelectric power. The structural studies showed that the Th${}_{2}$S${}_{3}$-type lattice is conserved under pressure, while it is subjected to an isostructural phase transition with a \ensuremath{\sim}0.7$%$ volume drop at 38.5 GPa. We speculated that this transition could be driven by the $s\ensuremath{\rightarrow}d$ electron transfer in the Ti atoms. For the Th${}_{2}$S${}_{3}$-type Ti${}_{2}$O${}_{3}$, we have established a bulk modulus value, ${B}_{0}$ $=$ 258.3 GPa at ${B}_{0}^{\ensuremath{'}}$ $=$ 4.1. A full profile analysis of the diffraction patterns allowed us to discover anomalies in the compression behavior of the Th${}_{2}$S${}_{3}$-type structure. The bond valence sums method suggested that at ambient conditions the Ti cations have predominantly Ti${}^{3+}$ oxidation state, but applied pressure stimulates a partial charge disproportionation between the Ti1 and Ti2 sites achieving the maximal effect---reduction of the Ti1 cations to \ensuremath{\sim}Ti${}^{2.5+}$ and oxidation of the Ti2 ones to \ensuremath{\sim}Ti${}^{3.5+}$ near 14 GPa. Pressure evolution of Raman spectra across the above crossovers showed distinct changes corroborating the above findings. The high-pressure electronic transport studies confirmed that the Th${}_{2}$S${}_{3}$-type Ti${}_{2}$O${}_{3}$ remains semiconducting up to 21 GPa at ambient and low temperatures down to 4.2 K. These studies found additional features, e.g., in the activation energy curve near 7 GPa, that is accompanied by inversion of the dominant conductivity type from electron to hole. The intriguing high-pressure behavior of Ti${}_{2}$O${}_{3}$ with the Th${}_{2}$S${}_{3}$-type structure can contribute to better understanding of high-pressure properties of transition-metal sesquioxides.

International audience; High pressure and high temperature x-ray absorption near edge spectroscopy experiments have been carried out on Ce60Al20Cu20 bulk metallic glass showing an electronic delocalization of the 4f-electron of cerium under pressure. In parallel, high pressure extended x-ray absorption fine structure spectroscopy reveals large structural modifications of the cerium local environment. This study provides experimental evidence that an electronic driven structural transformation occurs in cerium based bulk metallic glasses (Ce-BMGs). The effect of temperature on the hysteresis of this amorphous-amorphous phase transition is also discussed, suggesting the existence of a critical point in the phase diagram of Ce-BMGs. This work will encourage further investigations on Ce-based metallic glasses phase diagrams in order to support, or refute, the actual theoretical understanding of polyamorphism.

The high-pressure behavior of elemental Sn has been studied by angle-dispersive synchrotron x-ray diffraction up to 138 GPa under quasihydrostatic conditions at room temperature. The data confirm the occurrence of a first-order phase transition at 10.8 GPa between $\ensuremath{\beta}$-Sn (Sn-II) ($I{4}_{1}/amd$) and a further body-centered-tetragonal polymorph ($\ensuremath{\gamma}$-Sn or Sn-III) ($I4/mmm$). Above 32 GPa, this phase exhibits a distortion into a new body-centered-orthorhombic (bco) modification ($Immm$). Beyond 70 GPa, the structure becomes body-centered cubic (bcc) ($Im\ensuremath{-}3m$). There is a region of coexistence where the bcc reflections are observed to appear superimposed on the bco pattern above 40 GPa and the two diffraction signatures coexist until 70 GPa. We examined this possible existence of a kinetically hindered first-order phase transition between the two polymorphs by performing density functional theory (DFT) calculations with an emphasis on the potential energy in response to axial ($c/a,b/a$) distortions at constant volume. The DFT results suggest a slightly different interpretation of the structural transformations. At low pressure, the global minimum energy is always centered around $b/a=1$, and there is no indication of transformation to a bco structure. However, any small strains in the $c/a$ ratio in the system would provide an orthorhombic distortion of the observed magnitude. Such strains could be induced due to slight deviations from hydrostatic conditions in the experimental study. Concerning the possible bco-bcc phase transitions, the DFT calculations reveal an energy surface with a barrier developed between solutions with different $c/a$ values over the pressure range of interest. Crucially, the calculated barrier heights are low, and they disappear in the region of the observed phase transformation. The DFT results indicate a mechanically softened material that may exhibit localized domain structures in response to even slightly nonhydrostatic stress conditions.

Compressibility of high-purity nanostructured cBN has been studied under quasi-hydrostatic conditions at 300 K up to 35 GPa using diamond anvil cell and angle-dispersive synchrotron powder X-ray diffraction. It has been found that the data fit to the Vinet equation of state yields the values of the bulk modulus B₀ of 375(4) GPa with its first pressure derivative B₀´ of 2.3(3), thus, the nanometer grain size (≈ 20 nm) results in a decrease of the bulk modulus by ≈ 9‰. Сжимаемость высокочистого наноструктурированного cBN была изучена в квазигидростатических условиях при 300 K до 35 GPa в алмазных наковальнях с помощью угловой дисперсионной рентгеновской дифракции синхротронного излучения. Описание полученных данных уравнением состояния Винэ дает значение модуля сжимаемости B₀ = 375(4) ГПа и его первой производной по давлению B₀' = 2.3(3). Наноразмер зерна (~ 20 нм) приводит к уменьшению модуля сжимаемости на ~ 9 %. Стисливість високочистого наноструктурованого cBN була вивчена в квазігідростатичних умовах при 300 K до 35 ГПa в алмазних наковальнях за допомогою кутової дисперсійної рентгенівської дифракції синхротронного випромінювання. Опис одержаних даних рівнянням стану Віне дає значення модуля стисливості B₀ = 375(4) ГПа і його першої похідної по тиску B₀' = 2.3(3). Нанорозмір зерна (~ 20 нм) приводить до зменшення модуля стисливості на ~ 9 %.