Pressure-induced superconductivity in noncentrosymmetric heavy-fermion CeRhSi3

We report the pressure-induced superconductivity in the noncentrosymmetric heavy-fermion CeRhSi3. The superconductivity emerges above about 12 kbar even though the antiferromagnetic ordering persists. Furthermore, another anomaly is observed in the superconducting phase. The anomalous magnetic field-temperature phase diagram with a high upper critical field suggests that an unconventional superconductivity is realized in CeRhSi3.     

1H NMR study of [N(CH3)4]2ZnCI4 at high pressures and low temperatures

Wide-line proton NMR studies on polycrystalline tetramethylammonium tetrachlorozincate have been carried out at high hydrostatic pressures up to 15 kbar in the temperature range 77-300 K and at ambient pressure down to 4.2 K. A second-moment transition is observed to occur starting around 161 K, the temperature for the V-VI phase transition. This transition temperature is seen to have a negative pressure coefficient up to 2 kbar, beyond which it changes sign. At 77 K the second moment decreases to 4 kbar and then increases again as a function of pressure. The results are explained in terms of the dynamics of the N(CH₃)₄ groups.     

Anisotropy of Linear Thermal Expansion and Compressibility of Y 2 Fe 17 Under Pressure and its Correlation to Magnetic Structure

A complex temperature dependence of a.c. susceptibility of Y 2 Fe 17 under high pressures together with recent neutron diffraction studies under pressure proved the instability of the collinear ferromagnetic structure and the development of a non-collinear magnetic arrangement of Fe moments in Y 2 Fe 17 . To study the correlation between magnetic structure and volume in more detail we performed compressibility and linear thermal expansion studies under high pressures up to 100 kbar and 10 kbar, respectively. The compressibility in the paramagnetic state s P (above 10 kbar at room temperature) was determined from the Murnaghan equation of state using the X-ray data, \kappa_{P}=0.80\ {\rm Mbar}^{-1} . The linear thermal expansion and compressibility in the ferromagnetic state at low temperatures are highly anisotropic. As a consequence, the c/a ratio decreases with increasing pressure. The magnetic phase diagram of Y 2 Fe 17 compound was compiled up to 20 kbar.     

Neutron Diffraction Study of the p - T Phase Diagram for Erbium

Electrical resistivity measurements performed on a single crystal of erbium as a function of temperature and hydrostatic pressure have provided a preliminary p - T phase diagram. The results have been interpreted in terms of a model for the magnetic structures of Er deduced from neutron diffraction studies at ambient pressure. This model predicted the existence of a magnetic structure with a wave vector of Q =2/7 c * at 4.2 K, when the applied pressure is larger than 3 kbar. This paper reports a neutron diffraction study of erbium made in the temperature range of 4 to 100 K, at pressures between 0.5 and 6 kbar. We have observed the predicted suppression of the low temperature conical ferromagnetic phase and the emergence of a new phase with Q =8/33 c *. The neutron diffraction measurements has enabled us to identify the various phases that develop from the cycloidal phases previously observed at atmospheric pressure.     

Investigation of pressure induced electronic transitions in lanthanam,uranium and thorium

Pressure-induced transitions in lanthanum, uranium and thorium were investigated by measuring the room temperature thermoelectric power (S) of these elements in the pressure range zero to one hundred kbar in a Bridgman anvil apparatus. In lanthanum two isostructural electronic transitions that are precursors to the structural changes at 23 kbar and 62 kbar are observed. Subtle electronic transitions are observed in uranium and thorium at 43 kbar and 30 kbar respectively. A schematic phase diagram of lanthanum and its similarity to that of uranium is discussed.     

Neutron diffraction and electrical transport studies on the incommensurate magnetic phase transition in holmium at high pressures

Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Néel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.     

Raman spectra of phase a at various pressures and temperatures

Variations of the Raman spectra of phase A (Mg₇Si₂O₁₄H₆) were investigated up to about 400 kbar at room temperature and in the range 80–853 K at atmospheric pressure. Phase A appears to undergo a reversible phase transition around 180 kbar at room temperature, and it becomes amorphous above 813 K at atmospheric pressure. The Raman frequencies of the two strong OH bands of phase A decrease linearly with increasing pressure, but increase non-linearly with increasing temperature. The frequencies of the other Raman bands of phase A increase non-linearly with increasing pressure but decrease both linearly and non-linearly with increasing temperature within the experimental uncertainties and the range investigated. The trends of the pressure and temperature effects on the Raman frequencies of phase A parallel those observed in the hydrous β-phase, but nonlinear behaviour was not observed in the latter.     

Pressure dependence of the Raman scattering in the ordered phase of NH4Cℓ

We have observed Raman scattering in NH₄C? from 105K to 295K and up to 7kbar hydrostatic pressure, including the disordered phase II and the ordered phase IV. The pressure dependences of internal and lattice modes are reported, as well as that of the libration mode. The results are applied to several theories of the potential barrier to rotation.     

Superconductivity in polymeric sulfur nitride (SN)x at high pressure

Investigations of the pressure dependence of the superconducting transition temperature T_c up to 17 kbar, and of the normal conductivity up to 50 kbar are reported. It is observed that below 8 kbar, the value of T_c increases linearly with the pressure. In addition, there is a significant drop of T_c at about 9 kbar which may be due to a phase transition.     

Structural study of ND4I at high pressures and low temperatures

Abstract

Structure, positional, and thermal parameters of ND₄I were studied at high pressures up to 90 kbar and low temperatures down to 10 K using time-of-flight neutron diffraction. The phase transition from a disordered CsCI-type cubic phase ND₄I(II) into a recently discovered high pressure phase ND₄I(V) was observed at P = 80(5) kbar. Surprisingly, the structure of the high pressure phase V was found to bear a strong resemblance to that of the ambient pressure, low-temperature phase III - tetragonal structure with an antiparallel ordering of ammonium ions, space group P4/nmm. The critical value of the deuterium positional parameter corresponding to the II-V transition is close to the one for the phase transition between the disordered and ordered CsCl-type cubic phases II and IV in other ammonium halides.     

Effect of hydrostatic pressure on the Raman spectrum of anatase (TiO2)

Raman spectra of anatase have been investigated under pressures up to 60 kbar and at room temperature. A pressure-induced phase transition is observed at pressures above 25.6 kbar. The 197 cm^-1 mode (at 1 atm.) of six Raman active modes exhibits anomalous pressure dependence in which the frequency decreases with increasing pressure. This mode may be significant in the phase transition. The remaining modes show usual behavior.     

Pressure-induced phase transition in LiLuF4:Pr3+ investigated by an optical technique

The luminescence and luminescence kinetics of LiLuF(4) doped with 1.5 at.% of Pr(3+) obtained at high hydrostatic pressure changing from ambient to 220 kbar applied in a diamond anvil cell are presented. It has been shown that pressure causes shift of the emission lines toward the red with rates of the order of single cm(-1) kbar(-1). The pressure-induced phase transition from tetragonal to fergusonite structure for pressure above 100 kbar was observed. The crystal field calculations performed showed that this phase transition reduces the point symmetry of the Pr(3+) site from the S(4) to the C(2) point group.     

High pressure equation of state of rubidium

The pressure-volume relation of rubidium metal is studied by high-pressure x-ray diffraction up to 110 kbar at room temperature. In addition, pressure scans of the near-infrared reflectivity are recorded up to 250 kbar. Rubidium undergoes a bcc to fcc structural transition (Rb I → Rb II) at 70 ± 2 kbar. Other phase transitions occur at 128 ± 3, 160 ± 5 and 190 ± 5 kbar on the ruby pressure scale. The pressure-volume relation and the near-infrared reflectivity provide evidence for a pressure-induced 5s → 4d electronic transition similar to the well-known 6s → 5d transition in cesium metal.     

NMR study of ammonium halides under high pressure

Wide-line c.w. proton resonance investigations have been carried out on the ammonium halides, namely, ammonium chloride, ammonium bromide and ammonium iodide in the temperature range between 77 and 300 K and in the pressure range between 1 bar and 14 kbar. It has been found that the narrow iodide spectrum at 77 K broadens under the application of hydrostatic pressure. The barrier height for the ammonium ion motion in ammonium iodide under pressure has been estimated by carrying out a temperature variation study. The rotational potential for the motion of ammonium ion in ammonium iodide at 1 bar and 14 kbar has been calculated using earlier theoretical models and compared with values calculated for ammonium chloride and bromide. The barrier height in the case of ammonium iodide under pressure is found to be of the same order of magnitude as the value obtained in the case of ammonium bromide at atmospheric pressure indicating that the high pressure phase of ammonium iodide is likely to have the same structure as the low temperature ordered CsCl phase found in the case of the chloride and the bromide. The increase in the potential barrier height in the case of ammonium iodide under pressure indicates that the reorientational motion executed by the ammonium ions is inhibited by the application of pressure. This is also confirmed by the broadening of the spectral line at 77 K under the application of pressure.     

Pressure-induced phase transition in Sb2Te3

An anomalous change in electrical resistance with pressure was observed in crystalline Sb₂Te₃ around 80 kbar at room temperature. This anomaly was found to be closely related with a pressure-induced structural phase transition which is discovered by the present x-ray diffraction experiment.     

氨基酸DLH及其稀土镧配合物的高压红外和拉曼光谱研究

测定了DL-2-氨基-4-磺酸基-丁酸 [DLH, DL-Homocysteic acid, (NH+₃)-CH(COOH)-(CH₂)₂-SO-₃] 及其稀土La配合物[La(DLH)₂Cl₃·H₂O=LaL₂]在不同压力下的红外和拉曼光谱。DLH 在50 kbar左右压力以下存在两个压力诱导相转变区,它们分别在17和37 kbar左右,两者均为二级相转变,认为分子间氢键的存在是出现两个压力诱导相转变区的原因。在红外光谱中,SO-₃的对称伸缩振动的压力灵敏度(dν/dp)表现出与其他振动模式不同的变化趋势,它们在低压相区的平均压力灵敏度为0.30 cm-1·(kbar)-1、中压相区为0.32 cm-1·(kbar)-1、高压相区为0.41 cm-1·(kbar)-1,低压相区与高压相区的比值为0.72, 而其他振动模式刚好相反,低压相区与高压相区的比值为4.8。稀土La配合物LaL₂的生成,改变了分子间的氢键,在50 kbar左右压力以下只观察到1个压力诱导相转变区(27 kbar附近)。在红外光谱中,配合物LaL₂中SO-₃的反对称伸缩振动的压力灵敏度(dν/dp)也表现出与其他振动模式不同的变化趋势,它们在低压相区的平均压力灵敏度与高压相区的平均压力灵敏度的比值为0.43, 而其他振动模式的比值为2.5。     

Evidence of a medium-range ordered phase and mechanical instabilities in strontium under high pressure

We provided the first theoretical evidence for a medium-range ordered phase in high pressure strontium from the first-principles calculations. At the absolute zero temperature, the enthalpy–pressure relation shows that the bcc and hcp are energetically more favorable than the other experimentally observed phases between 24 and 27 GPa. In the present work, we concentrate on the bcc phase because we found a link to a medium-range ordered phase. Our results reveal that the bcc phonon dispersion at the N and H points starts softening at around 24.1 GPa. The ab initio molecular dynamics at 300 K and 27 GPa showed that the bcc is quickly transformed into a lower energy structure with R3c symmetry and distorted basis. The simulated diffraction patterns showed that the R3c structure has only a single major peak at low angle. The R3c peak locates near the first peak of the bcc structure. This is the evidence of the so-called medium-range ordered phase. This structure is a strong candidate for the unsolved S-phase reported by experiments.     

Pressure effect on the resistance of InS

The effect of pressure on the resistance of InS was studied to pressure higher than to 150 kbar for single crystal and to ca. 300 kbar for powdered samples. The resistance exhibits a sharp maximum at 47 kbar, which is explainable by the change of band structure due to pressure increase. Under higher pressure, the resistance decreased gradually with increasing pressure. A marked change in slope, however, was observed at 108 kbar, suggesting a phase transition possibly to a metallic phase.     

Effect of hydrostatic pressure on closed-loop phase behavior of block copolymers

The effect of hydrostatic pressure (P) on closed-loop phase behavior of deuterated polystyrene-block-poly(n-pentyl methacrylate) copolymers [dPS-PnPMA] was investigated by using small-angle neutron scattering and birefringence. For P<20.7 bar, dPS-PnPMA exhibited a lower disorder-to-order transition temperature (T(LDOT)) at 175 degrees C, and then an upper order-to-disorder transition temperature (T(UODT)) at 255 degrees C. With increasing pressure both T(LDOT) and T(UODT) were markedly changed, where dT(LDOT)/dP was 725 degrees C/kbar and dT(UODT)/dP was -725 degrees C/kbar. These are consistent with predictions by the Clausius-Clapeyron equation using measured values of the volume and enthalpy changes of both transitions. The large pressure coefficients imply that the closed-loop phase behavior observed for PS-PnPMA is an entropic-driven phase transition.     

The phase diagram of TTF-TCNQ under pressure

It is shown that the CDW-CDW interaction between TTF and TCNQ chains in TTF-TCNQ has a drastic pressure dependence changing its sign approximately at 5 kbar. This dependence determines the form of the phase transition curves on the T-P plane which turn out to be very similar to those observed experimentally. The recent experiments of Megtert et al. which established the existence of a T-P region where both systems of chains are ordered with a transverse period equal to 2a, may be explained by means of this interchain interaction pressure dependence together with CDW-impurity interaction.