Sharp Anomaly Research Articles

Observation of multiple dielectric relaxations in BaTiO3-Bi(Li1/3Ti2/3)O3 ceramics

Dense (1 − x)BaTiO3-xBi(Li1/3Ti2/3)O3 ceramics were fabricated by the solid state reaction route. Powder X-ray diffraction analyses revealed an increase in the unit cell volume with increasing x and a change on the average crystal structure from tetragonal (space group P4mm) to cubic ( $$ Pm\bar{3}m $$ ) at x > 0.10. Raman spectroscopy analyses corroborated a change of symmetry, but also showed the local structure for x > 0.10 to be inconsistent with the centrosymmetric ( $$ Pm\bar{3}m $$ ) space group. The dielectric measurements revealed for the first time, to our knowledge, a double relaxor behaviour in a BaTiO3-based solid solution. Basically, with increasing x, the sharp ferroelectric anomaly at the Curie temperature (T c) shifts towards lower temperatures until a relaxor-type response is observed, but simultaneously, another relaxation emerges above T c. The first arises from poor coupling between polar nanoregions, whereas the later obeys the Arrhenius Law and may be associated either with a defect-dipole reorientation or a Skanavi-type mechanism.

Electric field and aging effects of uniaxial ferroelectrics SrxBa1\u2212xNb2O6 probed by Brillouin scattering

Static and dynamic heterogeneity of disordered system is one of the current topics in materials science. In disordered ferroelectric materials with random fields, dynamic polar nanoregions (PNRs) appear at Burns temperature and freeze into nanodomain state below Curie temperature (TC). This state is very sensitive to external electric field and aging by which it gradually switches into macrodomain state. However, the role of PNRs in such states below TC is still a puzzling issue of materials science. Electric field and aging effects of uniaxial ferroelectric SrxBa1−xNb2O6 (x = 0.40, SBN40) single crystals were studied using Brillouin scattering to clarify the critical nature of PNRs in domain states below TC. On field heating, a broad anomaly in longitudinal acoustic (LA) velocity at low temperature region was due to an incomplete alignment of nanodomains caused by the interaction between PNRs. A sharp anomaly near TC was attributed to the complete switching of nanodomain to macrodomain state owing to the lack of interaction among PNRs. After isothermal aging below TC, the noticeable increase of LA velocity was observed. It was unaffected by cyclic temperature measurements up to TC, and recovered to initial state outside of a narrow temperature range above and below aging temperature.

Perovskite structure and low frequency relaxor- like- dielectric response of (Sr,Ce)TiO3 solid solution

Phase composition, structure stability, cations valance state, and relaxor-like-dielectric behavior of Sr(1–3/2x)CexTiO3 (SCT, x = 0.3, 0.4) solid solution were investigated systematically. The Sr(1–3/2x)CexTiO3 samples appear to be single phase within the detection limits of the technique, whereas the solid solution exhibits the higher angle doublet and triplet peak splitting associated with (200) and (321). X-ray photoelectron spectroscopy (XPS) analysis showed that the Ce substitution induces change in the cations valance state upon oxygen vacancies formation. The system exhibits features of low-frequency dependent relaxor-like-dielectric behavior rather than sharp frequency-independent anomalies. Besides this, two kind of relaxations were detected in the temperature range ≥ 350°C. According to the electric modulus and ac conductivity analysis, the relaxor-like-dielectric behavior results from the long-range conduction associated with ionized vacancies and mixed state of Ti3+/4+ and Ce3+/4+ cations.

Electronic and optical properties of BaTiO3 across tetragonal to cubic phase transition: An experimental and theoretical investigation

Temperature dependent diffuse reflectance spectroscopy measurements were carried out on polycrystalline samples of BaTiO3 across the tetragonal to cubic structural phase transition temperature (TP). The values of various optical parameters such as band gap (Eg), Urbach energy (Eu), and Urbach focus (E0) were estimated in the temperature range of 300 K to 480 K. It was observed that with increasing temperature, Eg decreases and shows a sharp anomaly at TP. First principle studies were employed in order to understand the observed change in Eg due to the structural phase transition. Near TP, there exist two values of E0, suggesting the presence of electronic heterogeneity. Further, near TP, Eu shows metastability, i.e., the value of Eu at temperature T is not constant but is a function of time (t). Interestingly, it is observed that the ratio of Eu (t=0)/Eu (t = tm), almost remains constant at 300 K (pure tetragonal phase) and at 450 K (pure cubic phase), whereas this ratio decreases close to the transition temperature, which confirms the presence of electronic metastability in the pure BaTiO3. The time dependence of Eu, which also shows an influence of the observed metastability can be fitted with the stretched exponential function, suggesting the presence of a dynamic heterogeneous electronic disorder in the sample across TP. First principle studies suggest that the observed phase coexistence may be due to a very small difference between the total cohesive energy of the tetragonal and the cubic structure of BaTiO3. The present work implies that the optical studies may be a sensitive probe of disorder/heterogeneity in the sample.

Enhanced thermopower and low thermal conductivity in p-type polycrystalline ZrTe5

Thermoelectric properties of polycrystalline p-type ZrTe5 are reported in the temperature (T) range of 2–340 K. Thermoelectric power (S) is positive and reaches up to 458 μV/K at 340 K on increasing T. The value of Fermi energy 16 meV suggests a low carrier density of ≈9.5 × 1018 cm−3. A sharp anomaly in S data is observed at 38 K, which seems intrinsic to p-type ZrTe5. The thermal conductivity (κ) value is low (2 W/m K at T = 300 K) with major contribution from the lattice part. Electrical resistivity data show the metal to semiconductor transition at T ∼ 150 K and non-Arrhenius behavior in the semiconducting region. The figure of merit zT (0.026 at T = 300 K) is ∼63% higher than that of HfTe5 (0.016) and better than those of the conventional SnTe, p-type PbTe, and bipolar pristine ZrTe5 compounds.

Genesis of tuff interval and its uranium enrichment in Upper Triassic of Ordos Basin, NW China

Recently measured high gamma ray values in the Yanchang Formation of the Upper Triassic in the Ordos Basin have added an interesting and controversial twist to the study of the formation’s uranium enrichment and genesis. High uranium and thorium contents in the tuffaceous layer cause high gamma ray values in the Yanchang Formation. Petrographic studies, major elements, rare earth elements (REEs), and trace elements have been systematically analyzed to determine the composition, geochemical environment, and diagenetic processes of the layer. The observed color of the tuffaceous layer in the study area varies from yellow to yellowish brown. The tuff consists of matrix supported with sub-rounded to sub-angular lithic fragments. These lithic fragments probably derived from pre-existing rocks and incorporated into the tuffaceous layer during volcanic eruption. Quartz, plagioclase, and biotite were observed in well to poorly sorted form, in addition to framboidal pyrite and organic laminae. Measured ratios of SiO2/Al2O3 ranged from 3.277 to 6.105 with an average of 3.738. The ratio of TiO2/Al2O3 varied from 0.037 to 0.201 with an average of 0.061, indicating that the sediments of the tuffaceous layer originated from an intermediate magma. REE distribution patterns show sharp negative Eu anomalies, indicating a reducing environment, which is suitable for uranium deposition. A reducing environment was confirmed by black shale in the base of the Yanchang Formation. Such black shale has high organic matter content that can take kerogene from mudstone and provide a reducing environment for uranium enrichment in the tuffaceous layer. Moreover, negative Eu anomalies and the REE patterns indicate a subduction-related volcanic arc environment as the magma source of the tuffaceous layers. High values of Rb, Ba, and Sr might be the result of fluid phase activities; low values of Hf and Eu indicate the involvement of crustal material during diagenesis of the tuff. Discrimination diagrams (Th/Yb vs Ta/Yb, Th/Hf vs Ta/Hf) suggest an active continental margin as the tectonic setting of source volcanoes. Plots of Nb versus Y, Rb versus Y + Nb, TiO2 versus Zr, and Th/Yb versus Nb/Yb of the tuffaceous content point to calc-alkaline continental arc-related magmatism. We concluded that uranium enrichment in the tuffaceous layer was supported by oxidation–reduction.

Cold plutonism in the Arabian–Nubian Shield: evidence from the Abu Diab garnet-bearing leucogranite, central Eastern Desert, Egypt

The Neoproterozoic Abu Diab garnet-bearing leucogranite (SiO 2 73.7 – 76.8 wt%; total alkalis 8.1 – 9.3 wt%) was emplaced during the late to post Pan-African Orogeny. The pluton is almost homogeneous in composition, weakly peraluminous (molecular Al 2 O 3 /(CaO + Na 2 O + K 2 O) = 1.04 – 1.12) and approaches the minimum melt composition in the water-saturated Qz–Ab–Or system. The chondrite-normalized patterns are almost unfractionated, with weak tetrad effects and prominent negative Eu anomalies. Ba, Sr, P, Eu and Ti show strong negative anomalies in primitive-mantle normalized multi-element diagrams. Magmatic garnet is dominantly a spessartine (66 – 67 mol %)–almandine (27 – 29 mol %) solid solution. Our results indicate that the Abu Diab granite magma formed from low-degree eutectic melting of a felsic pelite source in the lower to middle continental crust. Zirconium saturation thermometry indicates magma generation temperatures of 732 ± 28°C (2σ), placing the Abu Diab leucogranite in the ‘cold granite’ group. This indicates that muscovite breakdown is the dominant reaction in the melt source. The high normative Or, the increasing Rb/Sr concomitant with decreasing Sr and Ba, and the sharp negative Eu anomalies are consistent with fluid-absent melting. Field relations and petrographic observations indicate the emplacement of Abu Diab granites after the closure of the Mozambique Ocean and collision of East and West Gondwana, most probably during fast adiabatic uplift and decompression of the thickened crust. Supplementary material: The locations of the peraluminous leucocratic granites in the Arabian-Nubian and other supplementary data for this paper are available at https://doi.org/10.6084/m9.figshare.c.3815293 .

Field-induced phase diagram of the XY pyrochlore antiferromagnetEr2Ti2O7

We explore the field-temperature phase diagram of the XY pyrochlore antiferromagnet Er$_2$Ti$_2$O$_7$, by means of magnetization and neutron diffraction experiments. Depending on the field strength and direction relative to the high symmetry cubic directions $[001], [1\bar{1}0]$ and $[111]$, the refined field induced magnetic structures are derived from the zero field $\psi_2$ and $\psi_3$ states of the $\Gamma_5$ irreducible representation which describes the ground state of XY pyrochlore antiferromagnets. At low field, domain selection effects are systematically at play. In addition, for $[001]$, a phase transition is reported towards a $\psi_3$ structure at a characteristic field $H_c^{001}=$ 43 mT. For $[1\bar{1}0]$ and $[111]$, the spins are continuously tilted by the field from the $\psi_2$ state, and no phase transition is found while domain selection gives rise to sharp anomalies in the field dependence of the Bragg peaks intensity. For $[1\bar{1}0]$, these results are confirmed by high resolution inelastic neutron scattering experiments, which in addition allow us to determine the field dependence of the spin gap. This study agrees qualitatively with the scenario proposed theoretically by Maryasin {\it et al.} [Phys. Rev. B {\bf 93}, 100406(R) (2016)], yet the strength of the field induced anisotropies is significantly different from theory.

Structural evolution of MnTi0·8Ru0·2O3

Here, we present the structural studies on MnTi1-xRuxO3(x = 0, 0.2) compounds. The role of Ti ions in the magnetism of MnTiO3 was unclear so here this issue has been tried to address. The magnetic susceptibility (χ) data shows that the 3-dimensional magnetic character has been improved in the doped MnTiO3. The x = 0 compound goes paramagnetic to antiferromagnetic phase at a temperature ∼64 K followed by a broad peak at a temperature ∼100 K. But in x = 0.2 compound, the antiferromagnetic transition temperature has been shifted towards the lower temperature to ∼47.5 K with a broad peak at temperature ∼79 K. On the doping of Ru at Ti site a sharp anomaly in the temperature dependent magnetic susceptibility (χ) measurement is observed ∼47.5 K in the case of x = 0.2 compound. This sharp anomaly is attributed to the improved 3D character of magnetism which arises because of the direct exchange interaction between Mn-Ti/Ru ions in addition to the inter-layer super superexchange interaction between Mn-Mn ions via two intervening oxygen ions. It is interesting to note that even though the TN and T2D are at low temperatures compared to the x = 0 compound, the onset temperature of these two temperatures occurs at much higher temperature than as observed in x = 0 compound.

Spin gap in heavy fermion compound UBe13

Heavy fermion (HF) compounds are well known for their unique properties, such as narrow bandwidths, loss of coherence in a metal, non-Fermi-liquid behaviour, unconventional superconductivity, huge magnetoresistance etc. While these materials have been known since the 1970s, there is still considerable uncertainty regarding the fundamental mechanisms responsible for some of these features. Here we report transverse-field muon spin rotation (μ+SR) experiments on the canonical HF compound UBe13 in the temperature range from 0.025 to 300 K and in magnetic fields up to 7 T. The μ+SR spectra exhibit a sharp anomaly at 180 K. We present a simple explanation of the experimental findings identifying this anomaly with a gap in the spin excitation spectrum of f-electrons opening near 180 K. It is consistent with anomalies discovered in heat capacity, NMR and optical conductivity measurements of UBe13, as well as with the new resistivity data presented here. The proposed physical picture may explain several long-standing mysteries of UBe13 (as well as other HF systems).

Major, trace and rare earth element (REE) characteristics of tuffs in the Yenice-Saraycık area (Demirci, Manisa), Western Anatolia, Turkey

Geochemical investigation was carried out on tuffs intercalated with Neogene volcano-sedimentary rocks in the Yenice-Saraycık area (Demirci, Manisa), Turkey. The tuffs are classified as peraluminous and they show calc-alkaline character. They represent mainly rhyolitic to rhyodacitic composition.These silicic vitric tuffs are mostly either altered to zeolites (clinoptilolite–heulandite type) or clays. Their chondrite-normalized REE distribution patterns are remarkably similar. These patterns display light REE (LREE) enrichment with nearly flat heavy REE (HREE) and the strong negative Eu anomalies (Eu/Eu*=0.12–0.51). The existence of negative Eu anomaly is an indicator of feldspar fractionation. In primitive mantle-normalized diagram, all tuffs show nearly parallel patterns characterized by sharp negative anomalies of Nb, P and Ti along with positive anomalies of K and Pb. These findings demonstrate that they originated from a strongly evolved magma which was probably contaminated by crustal material. The negative Ti, Nb and P anomalies also show a subduction-related origin.On the other hand, the alteration of tuffs to zeolites has a prominent effect on their major, trace and REE abundances. Zeolitic tuffs are clearly enriched in Ca, Mg, P and LOI and depleted in Na, K and Mn when compared to unaltered tuff. They have also relatively lower U content but higher Ba, Sr, Cs, Pb, Zn, Ni, As and Sb. Furthermore, a little mobility of HREEs relative to LREEs is seen in most of the zeolitic samples. The loss of alkaline (Na+ and K+) and gain of alkaline-earth elements (Ca2+ and Mg2+) show that zeolitic alteration may have occurred under alkaline conditions. The source for the Ca2+ and Mg2+ gains is presumably groundwater circulating through the carbonate rocks of study area. The remarkable loss of U is probably related to the mobility of U during the alteration of vitric tuffs under the prevailing alkaline conditions. The significant increase of Ba, Sr, Cs, Pb, Zn, Ni, As and Sb in the zeolitic tuffs is most likely due to the ability of both zeolites and clays adsorb these elements.

Thermodynamic properties of antiferromagnetic ordered states ofπ−dinteracting systems ofκ−(BETS)2FeX4(X=Br,Cl)

The results are presented for systematic heat capacity measurements of \ensuremath{\pi}-$d$ interacting systems of $\ensuremath{\kappa}\ensuremath{-}{(\mathrm{BETS})}_{2}\mathrm{Fe}{\mathrm{Br}}_{4}$ and $\ensuremath{\kappa}\ensuremath{-}{(\mathrm{BETS})}_{2}\mathrm{FeC}{\mathrm{l}}_{4}$ [BETS = bis(ethylenedithio)tetraselenafulvalene] performed under in-plane magnetic fields. We observed sharp thermal anomalies at 2.47 K for $\ensuremath{\kappa}\ensuremath{-}{(\mathrm{BETS})}_{2}\mathrm{FeB}{\mathrm{r}}_{4}$ and at 0.47 K for $\ensuremath{\kappa}\ensuremath{-}{(\mathrm{BETS})}_{2}\mathrm{FeC}{\mathrm{l}}_{4}$ at 0 T that are associated with antiferromagnetic transitions of the $3d$ electrons in the anion layers. From analyses of the magnetic heat capacity data, we indicate that the two compounds show unconventional thermodynamic behaviors inherent in the \ensuremath{\pi}-d interacting layered system. In the case of $\ensuremath{\kappa}\ensuremath{-}{(\mathrm{BETS})}_{2}\mathrm{FeB}{\mathrm{r}}_{4}$, a small hump structure was observed in the magnetic heat capacity below the transition temperature when a magnetic field was applied parallel to the $a$ axis. In the case of $\ensuremath{\kappa}\ensuremath{-}{(\mathrm{BETS})}_{2}\mathrm{FeC}{\mathrm{l}}_{4}$, a similar hump structure was observed at 0 T that remained in the data with magnetic fields applied parallel to the $a$ axis. We demonstrate that the temperature dependencies of the magnetic heat capacities scale well by normalizing the temperatures with dominant one-dimensional direct interactions $({J}_{\mathrm{dd}}/{k}_{\mathrm{B}})$ of each compound. The field dependencies of the transition temperatures and the hump structures are elucidated in one simple magnetic field vs temperature ($H\ensuremath{-}T$) phase diagram. These results indicate that the thermodynamic features of both \ensuremath{\kappa}-type BETS salts are essentially equivalent, and the observed hump structures are derived from the one-dimensional ${J}_{\mathrm{dd}}$ interaction characters, which are still influential for magnetic features even in the long-range magnetic ordered states.

Modulated spin helicity stabilized by incommensurate orbital density waves in a quadruple perovskite manganite

Through a combination of neutron diffraction and Landau theory we describe the spin ordering in the ground state of the quadruple perovskite manganite ${\mathrm{CaMn}}_{7}{\mathrm{O}}_{12}$---a magnetic multiferroic supporting an incommensurate orbital density wave that onsets above the magnetic ordering temperature, ${T}_{\mathrm{N}1}=90$ K. The multi-$\mathbf{k}$ magnetic structure in the ground state was found to be a nearly-constant-moment helix with modulated spin helicity, which oscillates in phase with the orbital occupancies on the ${\mathrm{Mn}}^{3+}$ sites via trilinear magneto-orbital coupling. Our phenomenological model also shows that, above ${T}_{\mathrm{N}2}=48$ K, the primary magnetic order parameter is locked into the orbital wave by an admixture of helical and collinear spin density wave structures. Furthermore, our model naturally explains the lack of a sharp dielectric anomaly at ${T}_{\mathrm{N}1}$ and the unusual temperature dependence of the electrical polarization.

Single-gap superconductivity inβ−Bi2Pd

beta-Bi2Pd compound has been proposed as another example of a multi-gap superconductor [Y. Imai et al., J. Phys. Soc. Jap. 81, 113708 (2012)]. Here, we report on measurements of several important physical quantities capable to show a presence of multiple energy gaps on our superconducting single crystals of beta-Bi2Pd with the critical temperature Tc close to 5 K. The calorimetric study via a sensitive ac technique shows a sharp anomaly at the superconducting transition, however only a single energy gap is detected. Also other characteristics inferred from calorimetric measurements as the field dependence of the Sommerfeld coefficient and the temperature and angular dependence of the upper critical magnetic field point unequivocally to standard single s-wave gap superconductivity. The Hall-probe magnetometry provides the same result from the analysis of the temperature dependence of the lower critical field. A single-gapped BCS density of states is detected by the scanning tunneling spectroscopy measurements. Then, the bulk as well as the surface sensitive probes evidence a standard conventional superconductivity in this system where the topologically protected surface states have been recently detected by ARPES [M. Sakano et al., Nature Comm. 6, 8595 (2015)] .

Universal dynamic magnetism in Yb pyrochlores with disparate ground states

The ytterbium pyrochlore magnets, Yb2B2O7 (B = Sn, Ti, Ge) are well described by S_eff = 1/2 quantum spins decorating a network of corner-sharing tetrahedra and interacting via anisotropic exchange. Structurally, only the non-magnetic B-site cation, and hence, primarily the lattice parameter, is changing across the series. Nonetheless, a range of magnetic behaviors are observed: the low temperature magnetism in Yb2Ti2O7 and Yb2Sn2O7 has ferromagnetic character, while Yb2Ge2O7 displays an antiferromagnetically ordered Neel state at low temperatures. While the static properties of the ytterbium pyrochlores are distinct, inelastic neutron scattering measurements reveal a common character to their exotic spin dynamics. All three ytterbium pyrochlores show a gapless continuum of spin excitations, resembling over-damped ferromagnetic spin waves at low Q. Furthermore, the specific heat of the series also follows a common form, with a broad, high-temperature anomaly followed by a sharp low-temperature anomaly at T_C or T_N. The novel spin dynamics we report correlate strongly with the broad specific heat anomaly only, remaining unchanged across the sharp anomaly. This result suggests that the primary order parameter in the ytterbium pyrochlores associated with the sharp anomaly is "hidden" and not simple magnetic dipole order.

Gapless quantum excitations from an icelike splayed ferromagnetic ground state in stoichiometricYb2Ti2O7

The ground state of the quantum spin ice candidate magnet Yb2Ti2O7 is known to be sensitive to weak disorder at the 1 percent level which occurs in single crystals grown from the melt. Powders produced by solid state synthesis tend to be stoichiometric and display large and sharp heat capacity anomalies at relatively high temperatures, with Tc about 0.26 K. We have carried out neutron elastic and inelastic measurements on well characterized and equilibrated stoichiometric powder samples of Yb2Ti2O7 which show resolution-limited Bragg peaks to appear at low temperatures, but whose onset correlates with temperatures much higher than Tc. The corresponding magnetic structure is best described as an ice-like splayed ferromagnet. The spin dynamics in Yb2Ti2O7 are shown to be gapless on an energy scale smaller than 0.09 meV at all temperatures, and organized into a continuum of scattering with vestiges of highly overdamped ferromagnetic spin waves present. These excitations differ greatly from conventional spin waves predicted for Yb2Ti2O7 s mean field ordered state, but appear robust to weak disorder as they are largely consistent with those displayed by non stoichiometric crushed single crystals and single crystals, as well as by powder samples of Yb2Ti2O7 s sister quantum magnet Yb2Sn2O7.

Anomalous dielectric and piezoelectric properties and electrical conductivity of heavily doped LiNbO3:Zn crystals

In LiNbO3:Zn crystals with near-threshold doping levels ( 4.5–4.7 mol % Zn), high-temperature measurements and high-temperature annealing under short-circuit conditions lead to considerable changes in spontaneous unipolarity. The considerable changes in spontaneous unipolarity are accompanied by well-defined low-frequency dielectric dispersion and sharp anomalies in temperature dependences of electrical conductivity and dielectric permittivity. As a result, the piezoelectric modulus d333 increases to a level approaching the highest values reported in the literature for single-domain nominally pure LiNbO3 crystals.

Synthesis, crystal structure and magnetic properties of a new copper oxo-antimony sulphate CuSb6O8(SO4)2.

The new copper oxo-antimony sulphate CuSb6O8(SO4)2 crystallizes in the triclinic space group P1[combining macron] with the unit cell parameters a = 5.5342(4) Å, b = 7.6706(6) Å, c = 9.2374(7) Å, α = 96.505(5)°, β = 93.818(4)°, γ = 109.733(4)° and Z = 1. The crystal structure is made up of layers stacking along [001]. The layers are charge neutral and are connected to each other by only weak interactions. The copper atoms adopt a square planar [CuO4] coordination and such units are well separated from each other by corner and edge sharing to [SbO4] building blocks. The latter polymerize to form sheets with the formula [Sb3O8]∞. Sulphate groups connect to the antimony oxide sheets by corner sharing and are located at the interface of the layers. Above ∼10 K the magnetic susceptibility follows very well a Curie-Weiss law whereas below 10 K increasing deviations indicate the onset of antiferromagnetic correlations. Fitting the data in the range 10-50 K yields a Curie-Weiss temperature θ of -2.25(5) K. A sharp anomaly centered at TC = 0.67 K in the heat capacity data indicates long-range magnetic ordering. Short range antiferromagnetic correlations well above TC are seen in the magnetic contribution to the heat capacity and the magnetic susceptibility. These can be well described by the magnetism of a spin S = 1/2 Heisenberg chain with the nearest neighbor antiferromagnetic spin exchange interaction of Jintra = ∼2.8 K.

Crustal and uppermost mantle structure beneath the continental rifting area of the Gulf of Suez from earthquake tomography

Suez rift is one of the active seismic zones in the northward continuation of the Red Sea, as indicated by recent earthquake records from the Egyptian National Seismological Network (ENSN). We present a new model of P and S wave velocities in the crust and uppermost mantle beneath the Gulf of Suez and surrounding areas, including the northern portion of the Red Sea. Using the records from 94 seismic stations, we analyzed ~66,000 P and ~17,000 S wave arrival times from 9700 events. The travel time tomography inversion was performed using the iterative LOTOS code. The spatial resolutions of the derived models were assessed using several synthetic tests. The most prominent anomaly is a sharp high-velocity anomaly beneath the Red Sea, which is observed in both the P and S models at all depth intervals. We interpret this anomaly to be oceanic crust that was formed through extension associated with a dispersed system of spreading centers. Beneath the Gulf of Suez, the upper and middle crusts appear to be strongly heterogeneous and are dominated by low-velocity anomalies, indicative of the continental nature of the crusts. In contrast, at a depth of 30km, we observe a prominent high-velocity anomaly along Gulf of Suez, which is interpreted to be the result of crustal thinning associated with extension between the Sinai block and the African Plate. The thickness of the crust beneath the rift is estimated to be approximately 25km, whereas that in the surrounding areas appears to be 30–35km. In the northwestern part of the area, we observe a low-velocity zone in the middle and lower crusts that coincide with intense seismicity and a well-developed system of recent faults on the surface. This region may mark a possible area of northward propagation of the Suez Rift zone.

Pressure-induced electronic topological transition in Sb2S3

We report the high-pressure vibrational properties and a pressure-induced electronic topological transition in the wide bandgap semiconductor Sb2S3 (Eg = 1.7–1.8 eV) using Raman spectroscopy, resistivity and x-ray diffraction (XRD) studies. In this report, high-pressure Raman spectroscopy and resistivity studies of Sb2S3 have been carried out to 22 GPa and 11 GPa, respectively. We observed the softening of phonon modes , and B2g and a sharp anomaly in their line widths at 4 GPa. The resistivity studies corroborate this anomaly around similar pressures. The changes in resistivity as well as Raman line widths can be ascribed to the strong phonon–phonon coupling, indicating clear evidence of isostructural electronic topological transition in Sb2S3. The previously reported pressure dependence of a/c ratio plot obtained also showed a minimum at ~5 GPa consistent with our high-pressure Raman and resistivity results.