Rapid low-temperature densification of Ag2Se bulk material: mass transfer through the dissociative adsorption reaction of Ag protrusions and Se saturated vapor.

In materials science, the impact of density on a material's capabilities is profound. Conventional sintering requires high temperatures and is energy-demanding, propelling the pursuit of less intensive, low-temperature densification methods. Electric field-assisted sintering has recently gained attention for its simplicity and effectiveness, offering a new frontier in low-temperature densification. In this study, dense bulk materials were produced by subjecting monophasic Ag2Se powders to electric field-assisted sintering, where a direct current with an average value of 4 A was applied, achieving a peak temperature of 344 K. The novel low-temperature densification mechanism unfolds thus: nanoscale silver protrusions, stimulated by electrical current, engage in a dissociative adsorption reaction with the ambient saturated selenium vapor. This process swiftly engenders the formation of fresh silver selenide (Ag2Se) compounds, initiating nucleation and subsequent growth. Consecutively, these compounds seamlessly occupy and expand, perpetually bridging the interstices amidst the powders. In a scant 8 s, the density swiftly surpassed 99%, yielding a bulk material that exhibited aZTvalue of 1.07 at 390 K. This investigation not only attains an unparalleled density at low temperatures but also charts a pioneering course for material densification in such conditions.

Manipulating the Interfacial Band Bending For Enhancing the Thermoelectric Properties of 1T'-MoTe2 /Bi2 Te3 Superlattice Films.

Interfacial charge effects, such as band bending, modulation doping, and energy filtering, are critical for improving electronic transport properties of superlattice films. However, effectively manipulating interfacial band bending has proven challenging in previous studies. In this study, (1T'-MoTe2 )x (Bi2 Te3 )y superlattice films with symmetry-mismatch were successfully fabricated via the molecular beam epitaxy. This enables to manipulate the interfacial band bending, thereby optimizing the corresponding thermoelectric performance. These results demonstrate that the increase of Te/Bi flux ratio (R) effectively tailored interfacial band bending, resulting in a reduction of the interfacial electric potential from ≈127 meV at R = 16 to ≈73 meV at R = 8. It is further verified that a smaller interfacial electric potential is more beneficial for optimizing the electronic transport properties of (1T'-MoTe2 )x (Bi2 Te3 )y . Especially, the (1T'-MoTe2 )1 (Bi2 Te3 )12 superlattice film displays the highest thermoelectric power factor of 2.72 mW m-1 K-2 among all films, due to the synergy of modulation doping, energy filtering, and the manipulation of band bending. Moreover, the lattice thermal conductivity of the superlattice films is significantly reduced. This work provides valuable guidance to manipulate the interfacial band bending and further enhance the thermoelectric performances of superlattice films.

Corrigendum: Superparamagnetic enhancement of thermoelectric performance.

This corrects the article DOI: 10.1038/nature23667.

Superparamagnetic enhancement of thermoelectric performance.

The ability to control chemical and physical structuring at the nanometre scale is important for developing high-performance thermoelectric materials. Progress in this area has been achieved mainly by enhancing phonon scattering and consequently decreasing the thermal conductivity of the lattice through the design of either interface structures at nanometre or mesoscopic length scales or multiscale hierarchical architectures. A nanostructuring approach that enables electron transport as well as phonon transport to be manipulated could potentially lead to further enhancements in thermoelectric performance. Here we show that by embedding nanoparticles of a soft magnetic material in a thermoelectric matrix we achieve dual control of phonon- and electron-transport properties. The properties of the nanoparticles-in particular, their superparamagnetic behaviour (in which the nanoparticles can be magnetized similarly to a paramagnet under an external magnetic field)-lead to three kinds of thermoelectromagnetic effect: charge transfer from the magnetic inclusions to the matrix; multiple scattering of electrons by superparamagnetic fluctuations; and enhanced phonon scattering as a result of both the magnetic fluctuations and the nanostructures themselves. We show that together these effects can effectively manipulate electron and phonon transport at nanometre and mesoscopic length scales and thereby improve the thermoelectric performance of the resulting nanocomposites.

Electrically Tunable Antiferroelectric to Paraelectric Switching in a Semiconductor.

The monoclinic α-Cu2Se phase is the first multipolar antiferroelectric semiconductor identified recently by electron microscopy. As a semiconductor, although there are no delocalized electrons to form a static macroscopic polarization, a spontaneous and localized antiferroelectric polarization was found along multiple directions. In conventional ferroelectrics, the polarity can be switched by an applied electric field, and a ferroelectric to paraelectric transition can be modulated by temperature. Here, we show that a reversible and robust antiferroelectric to paraelectric switching in a Cu2Se semiconductor can be tuned electrically by low-voltage and high-frequency electric pulses, and the structural transformations are imaged directly by transmission electron microscopy (TEM). The atomic mechanism of the transformation was assigned to an electrically triggered cation rearrangement with a low-energy barrier. Due to differences of the antiferroelectric and paraelectric phases regarding their electrical, mechanical, and optical properties, such an electrically tunable transformation has a great potential in various applications in microelectronics.

Metallic Carbonitride MXene Based Photonic Hyperthermia for Tumor Therapy.

Photothermal therapy (PTT) as a noninvasive hyperthermia exhibits high potential for anti-cancer treatments. The explosion of efficient photothermal agents (PTAs) keeps developing rapidly. MXene stands out due to its intriguing structures, fantastic photodynamic properties, and good biocompatibility. However, the potential of MXenes has not been sufficiently explored in PTT. Its versatile chemical compositions of MXenes provide vast opportunities to discover new candidates. Considering that the metallic feature is mainly attributed to the metal element, anionic modulation may open a distinct avenue to propel efficient PTAs with metallic nature, which is expected for high light-harvesting over near-infrared (NIR)-I and NIR-II. As a paradigm, metal carbonitride is chosen to visualize the influences of anionic modulation. Taking advantage of electron injection from nitrogen, the distinct carbonitride Ti3 C1.15 N0.85 F0.88 O0.56 (OH)0.56 exhibits a strong NIR absorption (36.6 L g-1 cm-1 at 808 nm, 43.5 L g-1 cm-1 at 1064 nm), resulting in efficient photonic hyperthermia against tumors in vitro and in vivo. Looking through a large family of MXenes, this proof-of-principle demonstration offers a deep understanding between atomic composition and physicochemical properties, which further solidifies MXenes with all the potential for biomedical applications.

Psychological risk and protective factors associated with depression among older adults in mainland China: A systematic review and meta-analysis.

BACKGROUND: Although geriatric depression is a public health concern in mainland China, findings about its psychological risk and protective factors have been inconsistent, and its prevention programmes have been deficient. To improve interventions for geriatric depression, we designed a study to systematically estimate the effect size of those factors. METHODS: To identify psychological risk and protective factors of geriatric depression, we conducted two independent literature searches in English- and Chinese-language databases, and we used a random effects model to analyse effect sizes. RESULTS: We identified 15 psychological risk and protective factors in 66 studies. The pooled effect sizes between the factors and geriatric depression ranged from 0.129 to 0.567. Self-esteem displayed a large effect size with depression (r = -0.567), whereas medium-to-large effect sizes emerged between geriatric depression and negative perceptions of age (r = 0.452), resilience (r = -0.426), rumination (r = 0.432), neuroticism (r = 0.381), extraversion (r = -0.363), self-efficacy (r = -0.357), sense of control (r = -0.343), and negative coping strategies (r = 0.315). The sample's mean age, the percentage of women sampled, and the research quality of the studies significantly moderated certain associations. LIMITATIONS: Large heterogeneity, the inexplicability of causal relationships between the factors and geriatric depression, and the lack of generalisability to special groups limit our findings. CONCLUSIONS: Self-esteem and perceptions of age are potential targets for improving interventions for geriatric depression in mainland China, which should continue to be developed and assessed for their effectiveness.

Phototherapy Facilitates Tumor Recruitment and Activation of Natural Killer T cells for Potent Cancer Immunotherapy.

Adoptively transferred natural killer T (NKT) cells confer distinct cancer surveillance without causing obvious side effects, making them a promising candidate for cancer immunotherapy. However, their therapeutic efficacy is limited by inefficient tumor infiltration and inadequate activation in an immunosuppressive tumor microenvironment. To overcome these obstacles, we develop a strategy of using photothermal therapy (PTT) to promote the antitumor ability of adoptively transferred NKT cells. The transferred NKT cells are efficiently recruited to PTT-treated tumors in response to PTT-created inflammation. Moreover, PTT treatment promotes the activation of NKT cells and enhances the NKT cell-initiated immune cascade. As a consequence, the combined therapy of PTT plus NKT cell transfer exhibits excellent growth inhibition of local tumors. Moreover, it efficiently rejects distant tumors and elicits long-term immunological memory to prevent tumor recurrence. Overall, the current study opens new paths to the clinical translation of NKT cells for cancer immunotherapy.

The loss and return of self: An interpretative phenomenological analysis of coping and recovery from chronic hepatitis B in China.

Chronic hepatitis B (CHB) is a prevalent disease with various negative consequences. The lived experience of coping and recovery of a patient with Chronic hepatitis B was explored in this study. A semistructured interview was conducted with one participant who had been recovered from Chronic hepatitis B for 10 years. Data were analyzed using interpretative phenomenological analysis. Five superordinate themes emerged, including lingering in the shadow of death anxiety, diminished functioning of the self, adopting a highly disciplined lifestyle, receiving social support, and the return of the self with scars. The findings revealed that the disease is deeply associated with moral standing, which means the diagnosis of Chronic hepatitis B might imply a loss of moral face for Chinese people living with the condition. Our findings point to the need for increasing knowledge about chronic hepatitis B, decoupling the disease from a moral standpoint, and providing a supportive environment.

High-Performance Thermoelectric α-Ag9 Ga1-x Te6 Compounds with Ultralow Lattice Thermal Conductivity Originating from Ag9 Te2 Motifs.

We have determined the complex atomic structure of high-temperature α-Ag9 GaTe6 phase with a hexagonal lattice (P63 mc space group, a=b=8.2766 Å, c=13.4349 Å). The structure has outer [GaTe4 ]5- tetrahedrons and inner [Ag9 Te2 ]5+ clusters. All of the Ag ions are disorderly distributed in the lattice. Seven types of the Ag atoms constitute the cage-like [Ag9 Te2 ]5+ clusters. The highly disordered Ag ions vibrate in-harmonically, producing strong coupling between low frequency optical phonons and acoustic phonons. This in conjunction with a low sound velocity of 1354 m s-1 leads to an ultralow thermal conductivity of 0.20 W m-1 K-1 at 673 K. Meanwhile, the deficiency of Ga in Ag9 Ga1-x Te6 compounds effectively optimizes the electronic transport properties. Ag9 Ga0.91 Te6 attains a highest power factor of 0.40 mW m-1 K-2 at 673 K. All these contribute to a much-improved ZT value of 1.13 at 623 K for Ag9 Ga0.95 Te6 , which is 41 % higher than that of the pristine Ag9 GaTe6 sample.

Strong Anisotropy and Bipolar Conduction-Dominated Thermoelectric Transport Properties in the Polycrystalline Topological Phase of ZrTe5.

ZrTe5 has unique features of a temperature-dependent topological electronic structure and anisotropic crystal structure and has obtained intensive attention from the thermoelectric community. This work revealed that the sintered polycrystalline bulk ZrTe5 possesses both (020) and (041) preferred orientations. The transport properties of polycrystalline bulk p-type ZrTe5 exhibits an obvious anisotropic characteristic, that is, the room-temperature resistivity and thermal conductivity, possessing anisotropy ratios of 0.71 and 1.49 perpendicular and parallel to the pressing direction, respectively. The polycrystalline ZrTe5 obtained higher ZT values in the direction perpendicular to the pressing direction, as compared to that in the other direction. The highest ZT value of 0.11 is achieved at 350 K. Depending on the temperature-dependent topological electronic structure, the electronic transport of p-type ZrTe5 is dominated by high-mobility electrons from linear bands and low-mobility holes from the valence band, which, however, are merely influenced by valence band holes at around room temperature. Furthermore, external magnetic fields are detrimental to thermoelectric properties of our ZrTe5, mainly arising from the more prominent negative effects of electrons under fields. This research is instructive to understand the transport features of ZrTe5 and paves the way for further optimizing their ZTs.

Culturally adapted and lay-delivered cognitive behaviour therapy for older adults with depressive symptoms in rural China: a pilot trial.

BACKGROUND: Late-life depression issues in developing countries are challenging because of understaffing in mental health. Cognitive behavioural therapy (CBT) is effective for treating depression. AIM: This pilot trial examined the adherence and effectiveness of an eight-session adapted CBT delivered by trained lay health workers for older adults with depressive symptoms living in rural areas of China, compared with the usual care. METHOD: Fifty with screen-positive depression were randomly assigned to the CBT arm or the care as usual (CAU) arm. The primary outcomes were the session completion of older adults and changes in depressive symptoms, assessed using the Geriatric Depression Scale (GDS). RESULTS: The majority (19/24) of participants in the CBT arm completed all sessions. Mixed-effect linear regression showed that the CBT reduced more GDS scores over time compared with CAU. CONCLUSION: Lay-delivered culturally adapted CBT is potentially effective for screen-positive late-life depression.

Large Thermal Conductivity Drops in the Diamondoid Lattice of CuFeS2 by Discordant Atom Doping.

Doping in a lattice refers to the introduction of very small quantities of foreign atoms and has a generally small effect on decreasing the lattice thermal conductivity, unlike alloying which involves large fractions of other elements and strongly enhances point defect phonon scattering. Here, we report that, by alloying only 3% of In on the Cu sites of the diamond-like lattice of CuFeS2 chalcopyrite compound (Cu1-xInxFeS2, x = 0.03) has a disproportionally large effect in reducing the lattice thermal conductivity of the compound from 2.32 to 1.36 Wm-1K-1 at 630 K. We find that In is not fully ionized to +3 when on the Cu sublattice and exists mainly in the +1 oxidation state. The 5s2 lone pair of electrons of In+ makes this atom incompatible (referred to as discordant) with the tetrahedral geometry of the crystallographic site. This causes strong local bond distortions thereby softening the In-S and Cu-S chemical bonds and introducing localized low frequency vibrations. The latter couple with the base phonon frequencies of the CuFeS2 matrix enhancing the anharmonicity and decreasing the phonon velocity, and consequently the lattice thermal conductivity. The control material in which the In doping is on the Fe3+ site of the structure at the same doping level (and found in the site-compatible In3+ state), has a far smaller effect on the phonon scattering.

Origin of Intrinsically Low Thermal Conductivity in Talnakhite Cu17.6Fe17.6S32 Thermoelectric Material: Correlations between Lattice Dynamics and Thermal Transport.

Understanding the nature of phonon transport in solids and the underlying mechanism linking lattice dynamics and thermal conductivity is important in many fields, including the development of efficient thermoelectric materials where a low lattice thermal conductivity is required. Herein, we choose the pair of synthetic chalcopyrite CuFeS2 and talnakhite Cu17.6Fe17.6S32 compounds, which possess the same elements and very similar crystal structures but very different phonon transport, as contrasting examples to study the influence of lattice dynamics and chemical bonding on the thermal transport properties. Chemically, talnakhite derives from chalcopyrite by inserting extra Cu and Fe atoms in the chalcopyrite lattice. The CuFeS2 compound has a lattice thermal conductivity of 2.37 W m-1 K-1 at 625 K, while Cu17.6Fe17.6S32 features Cu/Fe disorder and possesses an extremely low lattice thermal conductivity of merely 0.6 W m-1 K-1 at 625 K, approaching the amorphous limit κmin. Low-temperature heat capacity measurements and phonon calculations point to a large anharmonicity and low Debye temperature in Cu17.6Fe17.6S32, originating from weaker chemical bonds. Moreover, Mössbauer spectroscopy suggests that the state of Fe atoms in Cu17.6Fe17.6S32 is partially disordered, which induces the enhanced alloy scattering. All of the above peculiar features, absent in CuFeS2, contribute to the extremely low lattice thermal conductivity of the Cu17.6Fe17.6S32 compound.

PVP intercalated metallic WSe2 as NIR photothermal agents for efficient tumor ablation.

Transition metal dichalogenides (TMDCs) with unique layered structures hold promising potential as transducers for photothermal therapy. However, the low photothermal conversion efficiency and poor stability in some cases limit their practical applications. Herein, we demonstrate the fabrication of ultrathin homogeneous hybridized TMDC nanosheets and their use for highly efficient photothermal tumor ablation. In particular, the nanosheets were composed of metallic WSe2 intercalated with polyvinylpyrrolidone (PVP), which was facilely prepared through a solvothermal process from the mixture of selenourea crystals, WCl6 powder along with PVP polymeric nanogel. Our characterizations revealed that the obtained nanosheets exhibited excellent photothermal conversion efficiency, therapeutic demonstration with improved biocompatibility and physiological stability attributing to the combined merits of metallic phase of WSe2 and hydrophilic PVP insertion. Both the histological analysis of vital organs and in vitro/in vivo tests confirmed the nanosheets as actively effective and biologically safe in this phototherapeutic technique. Findings from this non-invasive experiment clearly emphasize the explorable therapeutic efficacy of the layered-based hybrid agents in future cancer treatment planning procedures.

Rhombohedral to Cubic Conversion of GeTe via MnTe Alloying Leads to Ultralow Thermal Conductivity, Electronic Band Convergence, and High Thermoelectric Performance.

In this study, a series of Ge1-xMnxTe (x = 0-0.21) compounds were prepared by a melting-quenching-annealing process combined with spark plasma sintering (SPS). The effect of alloying MnTe into GeTe on the structure and thermoelectric properties of Ge1-xMnxTe is profound. With increasing content of MnTe, the structure of the Ge1-xMnxTe compounds gradually changes from rhombohedral to cubic, and the known R3m to Fm-3m phase transition temperature of GeTe moves from 700 K closer to room temperature. First-principles density functional theory calculations show that alloying MnTe into GeTe decreases the energy difference between the light and heavy valence bands in both the R3m and Fm-3m structures, enhancing a multiband character of the valence band edge that increases the hole carrier effective mass. The effect of this band convergence is a significant enhancement in the carrier effective mass from 1.44 m0 (GeTe) to 6.15 m0 (Ge0.85Mn0.15Te). In addition, alloying with MnTe decreases the phonon relaxation time by enhancing alloy scattering, reduces the phonon velocity, and increases Ge vacancies all of which result in an ultralow lattice thermal conductivity of 0.13 W m-1 K-1 at 823 K. Subsequent doping of the Ge0.9Mn0.1Te compositions with Sb lowers the typical very high hole carrier concentration and brings it closer to its optimal value enhancing the power factor, which combined with the ultralow thermal conductivity yields a maximum ZT value of 1.61 at 823 K (for Ge0.86Mn0.10Sb0.04Te). The average ZT value of the compound over the temperature range 400-800 K is 1.09, making it the best GeTe-based thermoelectric material.

Structure and Improved Thermoelectric Properties of Ag2 xCr2-2 xSe3 Compounds.

This work shows that the thermoelectric properties of Cr2Se3 material are improved by doping with Ag. The influence of doping with Ag on the phase composition, microstructure, and thermoelectric properties of Ag2 xCr2-2 xSe3 ( x = 0-0.02) compounds was thoroughly investigated. Ag atoms prefer to occupy the 6c Wyckoff position of the space group, accompanied expansion of the lattice and distortion of the octahedral structure units. The electrical conductivity increases at elevated temperature, while the lattice thermal conductivity decreases significantly through Ag doping, which is primarily attributed to the distorted structure and enhanced alloy scattering. Therefore, it produces a peak ZT value of 0.27 at 673 K for Ag0.04Cr1.96Se3, which shows an increase of 23% compared with that of the undoped Cr2Se3 compound.

Prevalence and influence factors of suicidal ideation among females and males in Northwestern urban China: a population-based epidemiological study.

BACKGROUND: Suicide is an urgent public health challenge for China. This study aims to examine the prevalence, influence factors, and gender differences of suicidal ideation among general population in Northwestern Urban China. METHODS: Data used in this study were derived from the third wave of a cohort study of a randomized community sample with 4291 participants (≥ 20 years) in 2008 in Lanzhou City and Baiyin City, Gansu Province. Data were collected via face-to-face interview by the trained interviewers. Descriptive analyses, chi-square tests and multivariate logistic regressions were performed by using Stata 12.0, as needed. RESULTS: The prevalence of 12-month suicidal ideation was 4.29%, there was no significant difference between males and females [5.04% vs 3.62%, Adjusted Odds Ratio (AOR) = 0.83, p = 0.351]. Several risk factors for suicidal ideation were confirmed, including being unmarried (AOR = 1.55, p = 0.030), having depression symptoms (AOR = 2.33, p < 0.001), having other insurance (AOR = 1.83, p = 0.01) or no insurance (AOR = 1.73, p = 0.024). In addition, several influence factors were significantly different in males and females, such as being currently married (unmarried vs married, AOR = 1.84, p = 0.027, for females; no difference for males), feeling hopeless (hopless vs hopeful, AOR = 1.92, p = 0.06, for females; no difference for males), having other insurances (having other insurances vs having basic employee medical insurance, AOR = 1.92, p = 0.044, for males; no difference for females), having debts (having debts vs no debts, AOR = 2.69, p = 0.001, for males; no difference for females), currently smoking (smoking vs nonsmoking, AOR = 3.01, p = 0.019 for females, no difference for males), and currently drinking (drinking vs nondrinking, AOR =2.01, p = 0.022, for males; no difference for females). DISCUSSION AND CONCLUSION: These findings suggested that comprehensive suicide prevention strategies should be developed or strengthened in order to prevent suicide ideation in China, and the gender-specific differences need to be explored through further researches.

Advanced thermoelectrics governed by a single parabolic band: Mg2Si(0.3)Sn(0.7), a canonical example.

The well-known single parabolic band (SPB) model has been useful in providing insights into the understanding of transport properties of numerous thermoelectric materials. However, the conduction and valence bands of real semiconductors are rarely truly parabolic which limits the predictive power of the SPB model. The coincidence of the band edges of two parabolic bands, a situation arising in Mg2Si1-xSnx solid solutions when x∼ 0.7, naturally makes the SPB approximation applicable to evaluate all transport parameters. We demonstrate this in the case of Bi-doped Mg2Si0.3Sn0.7 where the minima of the two conduction bands at the X-point of the Brillouin zone coincide. The combination of a large density-of-states effective mass m* ∼ 2.6 me arising from the enhanced valley degeneracy Nv, high mobility µd due to low deformation potential Ed (8.77-9.43 eV), and ultra-low alloy scattering parameter Ea (0.32-0.39 eV) leads to an outstanding power factor, PFmax∝ (m*)(3/2)µd, of up to 4.7 mW m(-1) K(-2) at around 600 K. The specification and improved understanding of scattering parameters using the SPB model are important and instructive for further optimization of the thermoelectric performance of n-type Mg2Si0.3Sn0.7.

Low effective mass and carrier concentration optimization for high performance p-type Mg2(1-x)Li2xSi0.3Sn0.7 solid solutions.

Mg2Si1-xSnx solid solutions are promising thermoelectric materials for power generation applications in the 500-800 K range. Outstanding n-type forms of these solid solutions have been developed in the past few years with the thermoelectric figure of merit ZT as high as 1.4. Unfortunately, no comparable performance has been achieved so far with p-type forms of the structure. In this work, we use Li doping on Mg sites in an attempt to enhance and control the concentration of hole carriers. We show that Li as well as Ga is a far more effective p-type dopant in comparison to Na or K. With the increasing content of Li, the electrical conductivity rises rapidly on account of a significantly enhanced density of holes. While the Seebeck coefficient decreases concomitantly, the power factor retains robust values supported by a rather high mobility of holes. Theoretical calculations indicate that Mg2Si0.3Sn0.7 intrinsically possesses the almost convergent double valence band structure (the light and heavy band), and Li doping retains a low density of states (DOS) on the top of the valence band, contrary to the Ga doping at the sites of Si/Sn. Low temperature specific heat capacity studies attest to a low DOS effective mass in Li-doped samples and consequently their larger hole mobility. The overall effect is a large power factor of Li-doped solid solutions. Although the thermal conductivity increases as more Li is incorporated in the structure, the enhanced carrier density effectively shifts the onset of intrinsic excitations (bipolar effect) to higher temperatures, and the beneficial role of phonon Umklapp processes as the primary limiting factor to the lattice thermal conductivity is thus extended. The final outcome is the figure of merit ZT ∼ 0.5 at 750 K for x = 0.07. This represents a 30% improvement in the figure of merit of p-type Mg2Si1-xSnx solid solutions over the literature values. Hence, designing low DOS near Fermi level EF for given carrier pockets can serve as an effective approach to optimize the PF and thus ZT value.