Pressure-Induced Re-Entrant Superconductivity in Transition Metal Dichalcogenide TiSe2.

Transition metal dichalcogenide TiSe2 exhibits a superconducting dome within a low pressure range of 2-4 GPa, which peaks with the maximal transition temperature Tc of ≈1.8 K. Here it is reported that applying high pressure induces a new superconducting state in TiSe2, which starts at ≈16 GPa with a substantially higher Tc that reaches 5.6 K at ≈21.5 GPa with no sign of decline. Combining high-throughput first-principles structure search, X-ray diffraction, and Raman spectroscopy measurements up to 30 GPa, It is found that TiSe2 undergoes a first-order structural transition from the 1T phase under ambient pressure to a new 4O phase under high pressure. Comparative ab initio calculations reveal that while the conventional phonon-mediated pairing mechanism may account for the superconductivity observed in 1T-TiSe2 under low pressure, the electron-phonon coupling of 4O-TiSe2 is too weak to induce a superconducting state whose transition temperature is as high as 5.6 K under high pressure. The new superconducting state found in pressurized TiSe2 requires further study on its underlying mechanism.

Modulation of electrical and thermal transports through lattice distortion in BaTi1-xNbxO3solid solutions.

The electron and heat transports in solids are through the movement of carrier electrons and quantized lattice vibrations (phonons), which are sensitive to the lattice distortion and ionized impurities, and are essential aspects for the development of novel thermoelectric materials. In this study, we systematically investigated the modulations of electrical and thermal conductivities of BaTi1-xNbxO3solid solution (BTNO, 0 ≤ x ≤ 1) epitaxial films. At room temperature, BaTiO3belongs to tetragonal perovskite and exhibits electron conduction through doubly degenerated Ti 3d-t2gorbitals upon doping, while BaNbO3belongs to cubic perovskite and exhibits metallic electron conduction through partially filled triply degenerate Nb 4d-t2gorbitals. By controlling the Ti/Nb ratio, we found a dual modulation effect on both the lattice structures and conduction band, which affects the electrical and thermal conductivities. Similar to the SrTi1-xNbxO3solid solution (STNO, 0 ≤ x ≤ 1) system, a phase transition was detected atx âˆ¼ 0.5, at which both the electron and heat transports exhibit abrupt changes. Unlike the transition in STNO, which was attributed to a polaronic phase transition, the transition in BTNO was due to contributions from both the lattice distortion and polaron effect. By controlling the lattice distortion, conduction band, and polaronic phase transitions, the electrical and thermal conductivity of BTNO epitaxial films are modulated within a much greater range than those of the STNO epitaxial films. Due to the double contribution of electron carriers and phonon to thermal conductivity (κ), the maximumκmodulation ratio of BTNO epitaxial films was ∼6.9. Our research provides an effective route to design electrical/thermal management materials.

A Retrospective Study on the Effects of Convalescent Plasma Therapy in 24 Patients Diagnosed with COVID-19 Pneumonia in February and March 2020 at 2 Centers in Wuhan, China.

BACKGROUND This retrospective study aimed to describe the effects of convalescent plasma therapy in 24 patients diagnosed with coronavirus disease 2019 (COVID-19) pneumonia due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during February and March 2020 in Wuhan, China. MATERIAL AND METHODS The confirmation of SARS-CoV-2 infection was made by the reverse transcription-polymerase chain reaction test. We retrospectively analyzed the clinical data and laboratory test reports of patients with severe COVID-19 pneumonia who received a convalescent plasma transfusion. RESULTS A total of 24 patients with COVID-19 pneumonia who were transfused with ABO-compatible convalescent plasma were enrolled in the study. Convalescent plasma transfusion showed an effective clinical outcome in 14 of 24 patients (an effective rate of 58.3%). No patients had an adverse reaction to the transfusion. Compared with before convalescent plasma transfusion, the lymphocyte count after convalescent plasma transfusion increased to a normal level (median: 0.80×109/L vs. 1.12×109/L, P=0.004). Other laboratory indicators such as white blood cells, high-sensitivity C-reactive protein, procalcitonin, alanine aminotransferase, and aspartate transaminase showed a decreasing trend after transfusion. CONCLUSIONS This retrospective observational clinical study showed that convalescent plasma therapy could have beneficial effects on patient outcomes. Recently, regulatory authorization has been given for the use of convalescent plasma therapy, and clinical guidelines have been developed for the collection and use of convalescent plasma and hyperimmune immunoglobulin in patients with COVID-19.

Tuning the Carrier Scattering Mechanism by Rare-Earth Element Doping for High Average zT in Mg3Sb2-Based Compounds.

Mg3Sb2-based compounds are promising thermoelectric materials because of their excellent thermoelectric performance, low cost, and good mechanical properties. In this work, Er, Dy, Gd, and Nd are all confirmed to be effective n-type dopants for optimizing the carrier concentration, increasing the density of states effective mass, and suppressing the ionized impurity scattering of Mg3Sb2-based compounds. By increasing the sintering temperature, a larger grain size can be achieved and can effectively improve the carrier mobility in the whole measured temperature range. As a result, maximum zT values above ∼1.6 at 673 K and average zTs above ∼1.0 between 300 and 673 K were achieved for Mg3.07Er0.03Bi0.5Sb1.5, Mg3.07Dy0.03Bi0.5Sb1.5, and Mg3.07Nd0.03Bi0.5Sb1.5. In addition, a high compressive strength of ∼180 MPa was obtained in Mg3.07Dy0.03Bi0.5Sb1.5. Therefore, rare-earth element-doped Mg3Sb2-based compounds are promising for thermoelectric applications.

Pressure-induced metal-insulator transition in oxygen-deficient LiNbO3-type ferroelectrics.

Hydrostatic pressure and oxygen vacancies usually have deleterious effects on ferroelectric materials because both tend to reduce their polarization. In this work we use first-principles calculations to study an important class of ferroelectric materials-LiNbO3-type ferroelectrics (LiNbO3as the prototype), and find that in oxygen-deficient LiNbO3-δ, hydrostatic pressure induces an unexpected metal-insulator transition between 8 and 9 GPa. Our calculations also find that strong polar displacements persist in both metallic and insulating oxygen-deficient LiNbO3-δand the size of polar displacements is comparable to pristine LiNbO3under the same pressure. These properties are distinct from widely used perovskite ferroelectric oxide BaTiO3, whose polarization is quickly suppressed by hydrostatic pressure and/or oxygen vacancies. The anomalous pressure-driven metal-insulator transition in oxygen-deficient LiNbO3-δarises from the change of an oxygen vacancy defect state. Hydrostatic pressure increases the polar displacements of oxygen-deficient LiNbO3-δ, which reduces the band width of the defect state and eventually turns it into an in-gap state. In the insulating phase, the in-gap state is further pushed away from the conduction band edge under hydrostatic pressure, which increases the fundamental gap. Our work shows that for LiNbO3-type strong ferroelectrics, oxygen vacancies and hydrostatic pressure combined can lead to new phenomena and potential functions, in contrast to the harmful effects occurring to perovskite ferroelectric oxides such as BaTiO3.