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Semiconducting manganese selenide (MnSe), crystalizing in a cubic structure with a wide band gap, is focused on in this work for its potential as an ecofriendly thermoelectric material. Pristine MnSe exhibits a low carrier concentration of ∼1.3 × 1017 cm−3 at room temperature, which can be dramatically increased to ∼2.6 × 1021 cm−3 primarily resulting from the Mn-vacancy introduced by Na-doping at Mn site. The broad range of carrier concentration not only enables a reliable prediction of the electrical transport properties using a single parabolic band (SPB) model with the acoustic scattering, but also provides a well understanding of its underlying material physics. Such a doping and the simultaneously induced Mn-vacancies provide additional phonon scattering, leading to a reduced lattice thermal conductivity of ∼1.2 W/m-K at high temperatures.

Intermetallic clathrates are materials characterized by a large cage structure where guest atoms can move anharmonically, providing these materials exotic thermoelectric properties. Unfortunately, the dynamical and atomic nature of the rattling phonons, and their interactions with the electronic structure, are not fully understood. Here, we report that a germanium isotope effect can trigger an inherent guest rattling and cage distortion in clathrate Ba8Ga16Ge30 (BGG). Raman-scattering spectroscopy and advanced electron microscopy demonstrate that the atomic germanium isotope effect induces an off-centre rattling at the 6d sites as well as a tetrakaidecahedron deformation which is anisotropic for n-type BGG but isotropic for p-type BGG. The present findings indicate that the large n-type germanium isotope effect arises from the strong electron-phonon coupling, which opens up a novel avenue for manipulating dynamical motions of phonons via atomic isotope engineering. Keywords: Thermoelectric, Clathrate, Isotope effect, Electron-phonon coupling

Introducing resonant levels is a potent strategy to improve the thermoelectric properties of the thermoelectric systems. However, the beneficial effect of resonant levels tends to be weakened with rising temperature for the PbTe system. This motivates us to introduce dynamic doping of Cu into Cr-doped n-type PbTe to achieve the fully optimized carrier transport over a wide temperature range. As a consequence, an extraordinary figure of merit, ZT of ∼ 0.55 at room temperature, a peak ZT of ∼ 1.31 at 773 K and an average ZT of ∼ 1.02 in the range of 323 to 823 K are obtained in the Pb0.975Cr0.025Te-0.2%Cu. Additionally, how co-doped of Cr and Cu contributes to suppressing thermal transports is still ambiguous. Herein, we employ comprehensive electron microscopy investigations to reveal that the synergistic incorporation of Cr and Cu into the PbTe matrix results in a series of phonon scattering sources, including massive point defects, high-density of nanoscale precipitates, microscale secondary phases, and dense grain boundaries, which can significantly reduce the lattice thermal conductivity by enhancing phonon scattering. This work clarifies the fundamental Cr-doping mechanism in PbTe and demonstrates that dynamic Cu-doping engineering is an effective approach to boosting thermoelectric performance, which should be applied in other thermoelectric materials.

Misfit-layered chalcogenide has captured large attention due to its unique opportunity for optimizing figure of merit zT originating from the natural superlattice structure. Existing strategies mainly focus on single element doping at cation site, while multisite alloying, especially for the doping at anion site, has not yet properly understood. In this work, chloride doping at anion site as a novel method is utilized to create excess electrons for manipulating the carrier concentration, thus achieving an advancement on electronic performance (up to 1.0 mW K−2 m−1) by ∼35% in oriented textured (SnS)1.2(TiS2)2 alloys. Such a chloride anion doping also enables a reduction on the lattice thermal conductivity to 0.82 and 0.35 W K−1 m−1 in the in-plane and out-of-plane directions, respectively. In addition, the multisite alloying strengthen the phonon scattering for a further reduction on lattice thermal conductivity, thus leading to an enhancement of thermoelectric performance. Consequently, a record zT∼0.45 is realized in the in-plane direction, which demonstrates (SnS)1.2(TiS2)2 based material as a promising thermoelectric candidate and the multisite alloying as an effective strategy for zT enhancement.

Dense potassium-doped tungsten (W–K) ingots with homogeneously dispersed nanoscaled bubbles were fabricated by spark plasma sintering (SPS) using Al–K–Si (AKS) doped tungsten powder. Parameters such as sintering temperature, holding time and sintering pressure were considered to tune the grain size, density, microhardness, bubble formation and impurity contents. In addition, a two-step sintering scheme was designed to reduce Al/Si impurity contents and enhance the density. The sample prepared by the two-step sintering scheme displays both inter- and intra-granular nanocomposites, which is expected to have better creep resistance, high bending strength and fracture toughness. Potassium was detected inside the bubbles, determining the crucial role in the bubble formation process, and thus leading to compatible properties as plasma-facing material.

A kind of uranium-selective sorbent has been studied using graphene oxide nanoribbons (GONRs) from the unzipping of multiwalled carbon nanotubes as a solid matrix and amidoxime (AO) as a functional group. Amidoxime-functionalized GONRs (AOGONRs) were successfully prepared by chemical grafting technology and characterized by scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy. The as-prepared AOGONRs were applied to adsorb U(VI) from aqueous solutions and exhibited a high sorption capacity towards U(VI) due to the strong chelation of AO to U(VI). It can be noted that the uranium sorption on the AOGONRs was pH-dependent, ionic strength-independent, fast, endothermic, spontaneous and a pseudo-second order process. The U(VI) sorption amount reached up to 2.112 mmol g−1 (502.6 mg g−1) at pH = 4.5 and T = 298 K. The sorption study performed in a simulated nuclear industry effluent demonstrated that the new sorbent had a desirable selectivity towards U(VI) ions over a range of competing metal ions. The results suggest that AOGONRs may be a potential and suitable candidate for the separation of U(VI) from various uranium-containing water samples.

Thermoelectric performance of Ca3Co4O9 system has been enhanced through the misplaced substitution with Cr doping at Ca-sites. The study of Cr doping at Co-sites has also been performed for comparing. Base on the analysis of the structural data, we conclude that the doped Cr ions should be in the form of Cr+6, and enter into Ca-sites of Ca2CoO3 layers in Ca3−xCrxCo4O9 lattice and Co-sites of CoO2 layers in Ca3Co3.90Cr0.10O9 lattice, respectively. As Cr ions are doped into Ca-sites in Ca3−xCrxCo4O9 lattice, both resistivity and thermopower increase obviously, while thermal conductivity decreases. Among all samples, Ca2.95Cr0.05Co4O9 shows the maximum ZT value, which is enhanced by 12% than that of Ca3Co4O9. The results show that the misplaced substitution with a proper Cr doping at Ca-sites is beneficial to the enhancement of the thermoelectric performance in Ca3Co4O9 system compared to the traditional idea: Cr doping at Co-sites, which is suggested to originate from the combined action of the carrier concentration, the electronic correlation, and the lattice disharmony.

The effect of Re and Pt doping on the structural, electrical and thermal transport properties of Ca3Co4−xMxO9 (0≤x≤0.2, M=Re and Pt) samples have been investigated systematically. As Re7+ or Pt4+ ions are doped into Ca3Co4O9 lattice, the resistivity and the metal–insulator-transition temperature increase monotonously with increasing x, indicating that both Re- and Pt-substitution can result in more stable spin-density-wave state. For Re-doped samples, the thermopower increases with increasing x, while the thermopower of Pt-doped samples decreases monotonously. Although the decreased thermal conductivity of both Re- and Pt-doped samples is beneficial to the thermoelectric performance, their ZT value decreases with increasing x. The result shows that both Re and Pt doping may indeed exert a significant influence in the structural and transport properties of Ca3Co4O9 system, which are suggested to originate from the variations of carrier concentration and electronic correlation induced by Re or Pt doping.

We report on the structural, electrical, and thermal transport properties of the single crystals of Bi2Sr2Co2−x Ir x O y (0 ≤ x ≤ 0.2). Large-sized (centimeter-level) and good-quality single crystals were grown by a modified flux method. The substitution of Ir ions for Co ones makes the in-plane resistivity ρ ab increase monotonically, whereas, the in-plane thermopower S ab initially increases and then decreases as x is larger than 0.1. Therefore, among all samples, the in-plane power factor P ab (=S ab 2 /ρ ab) of Bi2Sr2Co1.9Ir0.1O y would reach a maximum value of 116.4 μWm−1K−2 at 300 K and shows a significant improvement of about 20 % compared to that of the parent sample. Our results indicate that an appropriate doping of Ir ions at Co-sites may provide an effective way to enhance the thermoelectric performance of Bi2Sr2Co2O y system.

The effective mass of band structure has been proven as a key parameter determining the electrical transport properties of thermoelectrics. Concretely, low effective mass along the transport direction always accompanies with a high carrier mobility, as well as an excellent electronic performance. This work focuses on n-type CdSnAs2, possessing an intrinsically low effective mass, for its potential as a thermoelectric material. A single Kane band model with acoustic phonon scattering not only enables an assessment of the electrical transport properties, but also provides a well understanding of its underlying physics. Benefited by the low effective mass, an extremely high Hall mobility of ∼4500 cm2/V-s is obtained in polycrystalline CdSnAs2, experimentally leading to a high power factor of ∼12 μW/cm-K2 at 600 K. Based on the model, an excellent peak zT is expectable through minimizing lattice thermal conductivity and optimizing carrier concentration, which demonstrates it as a promising thermoelectric material.

The structure, magnetic, electrical and thermal transport properties of Ca 3 Co 4− x Sb x O 9 (0 ⩽ x ⩽ 0.2) have been investigated systematically. Base on the analysis of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the valence state of the doped Sb ions is suggested to be +3 in the x = 0.05 sample, and its content increases monotonously along with the gradual introduction of Sb 5+ ions as x further increases. The resistivity and the metal–insulator-transition temperature increase with increasing x , indicating the more stable spin-density-wave state in the Sb-doped samples. The thermopower decreases first as x = 0.05, and then increases monotonously with increasing x till to 0.15. The thermal conductivity decreases obviously due to Sb-doping. As a result, the Ca 3 Co 3.90 Sb 0.10 O 9 sample has the largest thermoelectric figure-of-merit ZT value of 0.012 at room temperature, which is about two times larger than that of Ca 3 Co 4 O 9 . The results are suggested to originate from the variations of carrier concentration and electronic correlation via Sb-doping with the different valence states.

(1− x )(0.75ZnAl 2 O 4 –0.25TiO 2 )– x SrAl 2 Si 2 O 8 (abbreviated as (1− x )ZAT– x SAS) ceramics were prepared by the solid-state reaction. The effects of SAS content on shrinkage, phase compositions, microstructure and microwave dielectric properties were investigated. It shows that SAS with a rare negative shrinkage characteristic can effectively adjust the shrinkage of the (1− x )ZAT– x SAS ceramics to near-zero value. In addition, ZnAl 2 O 4 spinel, TiO 2 rutile and SrAl 2 Si 2 O 8 monoclinic phases can coexist in the (1− x )ZAT– x SAS system, which is helpful to control the microwave dielectric properties and obtain a serial e r value from 3.56 to 12.20 by changing the phase composition. Therefore, (1− x )ZAT– x SAS could be a kind of zero-shrinkage and low-permittivity microwave dielectric ceramics for many potential applications in the future.

The structural, magnetic, electrical and thermal transport properties of the polycrystalline samples Ca3Co4−xInxO9 (x = 0, 0.05, 0.10, 0.15, and 0.20) have been investigated systematically. The results indicate that the In-substitution has a negative effect on the low-temperature ferrimagnetic transition and the propagation of spin-density-wave. All In-doped samples have a much larger resistivity than that of the un-doped sample. And the temperature region where the Fermi liquid transport mechanism dominates is remarkably widened via In-doping. However, for the In-doped samples, as the In-doped content increases, the value of resistivity ρ decreases monotonously and the electronic correlation in the system enhances. With the addition of In-ions in Ca3Co4O9 system, the thermopower S and the ZT value decrease. The results are suggested to originate from the variations of carrier concentration and lattice disharmony in this system induced by In-doping.

The effect of K doping on structural, electronic transport, magnetic and specific heat properties in 4d perovskites Ba1 − xKxMoO3 (0 ≤ x ≤ 0.2) has been investigated. Partial substitution of K+ ions for Ba2+ ions does not change the space group, but decreases the lattice parameter a monotonously. All samples exhibit metallic behavior in the whole measured temperature range. The K doping does not change the Pauli-paramagnetic behavior in high temperature region, but a weak ferromagnetic (FM) transition is induced at about 50 K, which can be related to the deficiency of Mo. With K-doping content increasing, the resistivity increases, while the magnetic susceptibility and electronic specific heat coefficient decrease. The results are discussed according to the electron localization due to the disorder effect induced by dopants and the decrease in the density of state (DOS) at Fermi surface.

Interplay among various collective electronic states such as charge density wave and superconductivity is of tremendous significance in low-dimensional electron systems. However, the atomistic and physical nature of the electronic structures underlying the interplay of exotic states, which is critical to clarifying its effect on remarkable properties of the electron systems, remains elusive, limiting our understanding of the superconducting mechanism. Here, we show evidence that an ordering of selenium and sulphur atoms surrounding tantalum within star-of-David clusters can boost superconductivity in a layered chalcogenide 1T-TaS2-xSex, which undergoes a superconducting transition in the nearly commensurate charge density wave phase. Advanced electron microscopy investigations reveal that such an ordered superstructure forms only in the x area, where the superconductivity manifests, and is destructible to the occurrence of the Mott metal-insulator transition. The present findings provide a novel dimension in understanding the relationship between lattice and electronic degrees of freedom.

A series of $1T$-Fe$_x$Ta$_{1-x}$SSe (0 $\leq x \leq$ 0.1) single crystals was fabricated via the chemical-vapor-transport (CVT) method and investigated by structure, transport, and magnetic measurements along with the density-functional-theory (DFT) calculations. The superconductivity (SC) in parent $1T$-TaSSe can be gradually suppressed by Fe-substitution ($x\leq0.03$), accompanied by the disappearance of charge-density-wave (CDW). DFT calculations show that the Fe-substitution effectively inhibits the CDW superstructure and thereby the CDW domains are destroyed. With further increasing $x$ ($x>0.03$), the disorder-induced scattering increases, and the system enters into the possible Anderson localization (AL) state. Our results prove the SC develops in the CDW phase and coexists with the CDW domain in $1T$-TaSSe system.

1 Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China 2 Frontier Research Center, Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8503, Japan 3 Advanced Solid State Chemistry Laboratory, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan 4 Laboratory for Pohang Emergent Materials, Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea

BiFeO3 films are prepared directly on n-type Si (100) substrates using chemical solution deposition method. The effects of individual-layer thickness via controlling the solution concentration on the texture, morphology, magnetic properties as well as the magnetoelectric properties are investigated. It was first observed that the derived films are the highly preferred c-axis oriented on Si substrates. With decreasing individual-layer thickness, the c-axis texture is improved due to preferred nucleation at the interfaces. The magnetization and the dielectric constant is increased and decreased with decreasing individual-layer thickness, respectively. It is interesting to observe that the magnetoelectric coupling is obviously enhanced with decreasing individual-layer thickness, which is beneficial for potential applications.

Chemical solution deposition as a simple method for preparation of oxide films is used to fabricate misfit structured Ca3Co4O9 thermoelectric films using cheap precursors, Ca and Co acetates, which opens up a simple route to fabricate large-area Co-based oxide thermoelectric films. The results show that when the annealing temperature is higher than 800°C crystallized Ca3Co4O9 films can be obtained on single-crystal LaAlO3 substrates, whereas the Ca3Co4O9 films are amorphous for lower annealing temperatures. Experimental evidence shows that the amorphous Ca3Co4O9 films behave like semiconductors with enhanced resistivity and Seebeck coefficient within the measured temperature range. The magnetoresistance is positive indicating the absence of long-range order of the Co-ion spins. For the crystallized Ca3Co4O9 films, it can be seen that the thinner films show the characteristics of spontaneous dewetting induced by the stress, which suggests that it is possible to prepare nanostructured Ca3Co4O9 films through...