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Thermoelectric technology enables the direct interconversion between heat and electricity. SnSe has received increasing interest as a new promising thermoelectric compound due to its exceptionally high performance reported in crystals. SnSe possesses intrinsic low thermal conductivity as a congenital advantage for thermoelectric, but high thermoelectric performance can be hardly achieved due to the difficulty to realize efficient doping to raise its low carrier concentration to an optimal level. In this work, it is found that a series of rare earth elements are effective dopants for SnSe, which can greatly improve the electrical transport properties of p‐type polycrystalline SnSe. In particular, the remarkable enhancement in electrical conductivity and power factor is achieved by Na/Er co‐doping at 873 K. The lattice thermal conductivity is reduced due to the presence of abundant defects (dislocations, stacking faults, and twin boundaries). Consequently, a peak thermoelectric figure of merit ZT (2.1) as well as a high average ZT (0.77) are achieved in polycrystalline SnSe. [ABSTRACT FROM AUTHOR]

GeTe and (Bi,Sb)2Te3 are two representative thermoelectric (TE) materials showing maximum performance at middle and low temperature, respectively. In order to achieve higher performance over the whole temperature range, their segmented one‐leg TE modules are designed and fabricated by one‐step spark plasma sintering (SPS). To search for contact and connect layers, the diffusion behavior of Fe, Ni, Cu, and Ti metal layers in GeTe is studied systematically. The results show that Ti with a similar linear expansivity (10.80 × 10−6 K−1) to GeTe, has low contact resistance (3 µΩ cm2) and thin diffusion layer (0.4 µm), and thus is an effective metallization layer for GeTe. The geometric structure of the GeTe/(Bi,Sb)2Te3 segmented one‐leg TE module and the ratio of GeTe to (Bi,Sb)2Te3 are determined by finite element simulation method. When the GeTe height ratio is 0.66, its theoretical maximum conversion efficiency (ηmax) can reach 15.9% without considering the thermal radiation and thermal/electrical contact resistance. The fabricated GeTe/(Bi,Sb)2Te3 segmented one‐leg TE module showed a ηmax up to 9.5% with a power density ≈ 7.45 mW mm−2, which are relatively high but lower than theoretical predictions, indicating that developing segmented TE modules is an effective approach to enhance TE conversion efficiency. [ABSTRACT FROM AUTHOR]

The past two decades have seen a great enhancement of piezoelectric coefficients (d33) to higher than 570 pC/N in (K, Na)NbO3 (KNN) piezoelectrics, but one notoriously unresolved issue is their severe temperature instability, obstructing them toward practical applications. The present work demonstrates a facile approach to overcome this problem by introducing a layered distribution of key dopants (Li and Sb) in a monolithic ceramic, featuring stepwise varied polymorphic phase transition (PPT) temperatures along the thickness direction. The dopant‐graded ceramic exhibits an outstanding d33 of 508 pC/N and a very large piezoelectric strain (Suni, of 0.18%). More importantly, an excellent temperature stability (d33 variation within 13% over the temperature range of 25–150 °C) is achieved, which is superior to that of most state‐of‐art KNN counterparts. These are attributed to the construction of spatially diffused PPT in combination with enhanced polarization, permittivity, and piezoresponse through interfacial effect, including the Maxwell–Wagner effect and intergranular stress by gradient doping. The results offer an alternative strategy for designing high‐performance piezoelectric materials with desirable temperature reliability. [ABSTRACT FROM AUTHOR]

BiFeO3‐BaTiO3 ceramics are promising lead‐free piezoelectric ceramics due to their high piezoelectric properties and high Curie temperature, but their high leakage current density makes the poling difficult. In this study, a decreased leakage current density by three orders of magnitude was obtained in Bi0.5Na0.5TiO3 (BNT) added 0.67BiFeO3‐0.33BaTiO3 (BF‐BT) ceramics. It was found that the largely improved insulating properties benefit from the reduced oxygen vacancies and weak reduction of Fe3+ to Fe2+ as confirmed by photoluminescence and X‐ray photoelectron spectroscopy measurements, thereby contributing to high‐temperature and high‐field poling. In addition, the introduction of BNT leaded to increased grain size. Due to the grown grains as well as reduced oxygen vacancies and Fe2+, enhanced insulating and optimal piezoelectric properties with Pr = 24.2 µC/cm2, d33 = 183 pC/N, kp = 0.28, and TC = 467°C were achieved in BF‐BT‐0.05BNT ceramics. [ABSTRACT FROM AUTHOR]

A series of Li2 CO3-added ( Ba0.95 Ca0.05)( Ti0.90 Sn0.10) O3 ( BCTS) ceramics were prepared by normal sintering at a low temperature of 1300°C; Their microstructure and electrical property evaluation were investigated with special emphases on the effect of Li2 CO3 addition. Adding Li2 CO3 significantly improves the sinterability of BCTS ceramics, resulting in a reduced sintering temperature by more than 150°C. The coexistence of R and T phases is confirmed by the Raman spectrum at room temperature for all samples and at a temperature range from −80°C to 40°C for sample with 3% mol Li2 CO3 addition. The specific ratio of R to T phase decreases with increasing temperature or Li2 CO3 addition. A higher εr is observed in T phase compared to R phase in the studied BCTS system. Better properties with d33 = 485 pC/N, kp = 39%, and Qm = 191 were obtained for BCTS sample with 3% mol Li2 CO3 addition, which is attributed to the increased grain size and density along with the variation in the specific ratio of R to T phase. [ABSTRACT FROM AUTHOR]

Various CuS nanostructures, including nanoflowers, doughnut-shaped nanospheres, dense nanospheres, and mixtures of nanoneedles, nanoparticles, and nanoplates, were synthesized from different copper and sulfur sources by a solvothermal method. The formation mechanisms along with photocatalytic properties for the degradation of rhodamine B (RhB) under visible-light irradiation were investigated in this study. The experimental results indicate that when the sulfur source is fixed at CS(NH2)2 in the solvothermal reaction, spherical nanoflowers, doughnut-shaped nanospheres, and dense nanospheres could be synthesized by using CuCl2, Cu(NO3)2, and CuSO4 as the copper source, respectively. Furthermore, atypical nanoflowers and a mixture of nanoneedles, nanoparticles, and nanoplates could be obtained when the sulfur source was switched to Na2S2O3 and Na2S with a fixed copper source of CuCl2. The energy gaps calculated from the light absorption spectrum were 1.61, 1.93, 2.01, 1.70, and 1.82 eV for the spherical nanoflowers, doughnut-shaped nanospheres, dense nanospheres, atypical nanoflowers, and the mixture of nanoneedles, nanoparticles, and nanoplates respectively. Among these five samples, three powders composed of spherical nanoflowers, atypical nanoflowers as well as a mixture of nanoneedles, nanoparticles, and nanoplates exhibited excellent photocatalytic properties and can degrade rhodamine B completely in an hour. [ABSTRACT FROM AUTHOR]

BaCa xTiO3-0.04LiF (0.010 ≤ x ≤ 0.045) ceramics were prepared by normal sintering at 1100 °C in air. A two-phase coexisted region across orthorhombic and rhombohedral symmetry was designed by refining the components. The detailed phase structure was analyzed quantitatively by the Rietveld refinement. BaCa0.035TiO3-0.04LiF ceramic showed better properties with d33 = 354 pC N−1, kp = 39%, Qm = 314, and TC = 65 °C, in which the relative proportion of rhombohedral symmetry was 74.86%, the grain size was 6.0 µm and the relative density was 91%, indicating that the synergistic effect of the phase structure, fine grain, and relatively high density contributed to the outstanding piezoelectric properties. [ABSTRACT FROM AUTHOR]

Polycrystalline Cu1.8S composites dispersed with nanoscale (∼50 nm) and microscale (∼200 µm) SiO2 were fabricated by combining mechanical alloying (MA) and spark plasma sintering (SPS) method. The average grain size of the host Cu1.8S bulk is refined from 700 nm to about 500 and 50 nm by dispersing micro- and nano-SiO2 along with a fragmented SiO2 particle itself from the raw size of 200 µm and 50 nm to 2 µm and 20 nm, respectively. The Seebeck coefficient increases by dispersing SiO2 particles in the whole measuring temperature interval and reaches the peak value 88 µV K−1 at 623 K for the nano-SiO2 dispersed sample. The thermal conductivity κ ranges from 1.14 to 1.54 W m−1 K−1 by raising the temperature from 323 to 623 K for the nano-SiO2 dispersed sample, which is lower than that of pure Cu1.8S owing to the strong phonon scattering. The micro-SiO2 dispersed sample has a high κ, ranging from 1.6 to 2.2 W m−1 K−1 at the same temperature range due to the large intrinsic κ of micro-SiO2 particles. A maximum thermoelectric figure of merit value of 0.28 was attained at 623 K in the nano-SiO2 dispersed sample. [ABSTRACT FROM AUTHOR]

( Ba1− x Ca x)( Ti0.92 Sn0.08) O3 ( x = 0.00-0.06 mol) ceramics with a high relative density over 96% were prepared by a conventional sintering method at 1480°C. At room temperature, a polymorphic phase transition from orthorhombic phase to tetragonal phase was confirmed by the XRD patterns in the composition range of 0.04 ≤ x ≤ 0.06. A high piezoelectric coefficient d33 up to 568 pC/N was obtained at x = 0.05 mol, which is higher than the other component of ( Ba, Ca)( Ti, Sn) O3 system. At the same time, the corresponding planar electromechanical coupling factor kp, converse piezoelectric coefficient dS/ dE, and dielectric constant εr reach 47.7%, 1013 pm/V, and 23000, respectively. These results indicate that the ( Ba, Ca)( Ti, Sn) O3 ceramics are a promising candidate to replace for the lead-based piezoelectric materials. [ABSTRACT FROM AUTHOR]

Hydrothermal method, which provides an effective approach to produce pure-phase BiFeO3-based solid solution was used to synthesize BiFeO3-BaTiO3 powders. The phase evolution was found to be connected with reaction temperature, initial KOH concentration, and duration time. The results show that perovskite cubic 0.5 BiFeO3-0.5 BaTiO3 crystallites can be synthesized at a temperature as low as 200°C, with a KOH concentration of 4 M. It indicates that the hydrothermal reactions responsible for the formation of crystalline BiFeO3-BaTiO3 are closely related to metal hydroxides dissolution and crystallization process. Field-emission scanning electron microscopy observations revealed a homogeneous distribution of submicron-sized BiFeO3-BaTiO3 powders. Ferroelectricity was demonstrated for the BiFeO3-BaTiO3 powders by polarization-electric field hysteresis loop measured with the corresponding bulk samples. [ABSTRACT FROM AUTHOR]

Lead-free Li-doped (Na,K)NbO3 ceramics with codopants of Ta and Sb with a nominal composition of [(Na0.535K0.480)0.942Li0.058](Nb0.86Ta0.10Sb0.04)O3 were prepared by normal sintering. The microstructure and piezoelectric, ferroelectric, and dielectric properties were investigated, with a special emphasis on the influence of sintering temperature from 1070° to 1100°C. All samples showed a pure pervoskite phase with tetragonal symmetry. The microstructure became denser but the volatilization of Na and K became intense on increasing the sintering temperature. Despite the absence of MPB-like transitional behavior, the piezoelectric coefficient ( d33), electromechanical coupling coefficient ( kp), and dielectric constant (ℇ) showed peak values of 264 pC/N, 35.6%, and 689.4, respectively, which were obtained in the sample sintered at 1090°C, and its Curie temperature ( TC) was about 338°C. An even higher d33 value can be expected if the MPB-like transitional composition range is further determined by compensating the Na and K contents. [ABSTRACT FROM AUTHOR]

A correction of the article "Effect of Ta Content on Phase Structure and Electrical Properties of Piezoelectric Lead-Free [(Na0.535K0.480)0.942Li0.058](Nb1− xTa x)O3 Ceramics" published in a prior issue is presented.