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In the present era of advanced technology, the surge for suitable multifunctional materials capable of operating above 300 °C has increased for the utilization of high-temperature piezoelectric devices. For this purpose, a pseudo-tetragonal phased CaBi4Ti3.98 (Nb0.5Fe0.5)0.02O15:xwt%MnO2 (CBTNF:xMn), with x = 0–0.20, ceramic system has been engineered for the investigation of structural, ferroelectric, dielectric and high-temperature-dependent piezoelectric properties. XRD analysis confirms that low-content Mn-ion insertion at the lattice sites of CBTNF does not distort the pseudo-tetragonal phase lattice of CBTNF:xMn ceramics, but enhances the functional behavior of the ceramic system, specifically at x = 0.15 wt%Mn. Compared to pure CBT and CBTNF ceramics, CBTNF:0.15Mn has demonstrated a highly dense relative density (~96%), a saturated polarization (PS) of 15.89 µC/cm2, a storage energy density (WST) of ~1.82 J/cm3, an energy-conversion efficiency (ƞ) of ~51% and an upgraded piezoelectric behavior (d33) of 27.1 pC/N at room temperature. Sharp temperature-dependent dielectric constant (εr) peaks display the solid ferroelectric behavior of the CBTNF:0.15Mn sample with a Curie temperature (TC) of 766 °C. The thermally stable piezoelectric performance of the CBTNF:0.15Mn ceramic was observed at 600 °C, with just a 0.8% d33 loss (25 pC/N). The achieved results signify that multi-valence Mn ions have effectively intercalated at the lattice sites of the pseudo-tetragonal phased CBTNF counterpart and enhanced the multifunctional properties of the ceramic system, proving it to be a durable contender for utilization in energy-storage applications and stable high-temperature piezoelectric applications.

Depolarization in the ceramic materials has remained the longstanding obstacle for the materials to be utilized in high-temperature piezoelectric devices. Herein, a strategy to defer thermal depolarization is employed. To acquire the best merits of two different materials, 0–3 type CaBi2Nb2O9:xwt%BiFeO3 (CBN:xwt%BFO) composites are engineered in a unique way by embedding the isolated BiFeO3 (BFO) grains at the grain boundaries of the CaBi2Nb2O9 (CBN) matrix. The composite with 0–3 type connectivity (CaBi2Nb2O9:40wt%BiFeO3) exhibits a high density of 7.98 g/cm3, a high saturated polarization of ~19 μC/cm2, high resistivity of ~1010 Ω.cm, and an enhanced piezoelectric coefficient d33 of 29 pC/N at room temperature. Composite shows the sharp-peaked ferroelectric–paraelectric transition at high Curie temperature TC of ~881°C. Importantly, the composite maintains a very high resistivity of ~105 Ω.cm even at 500°C and the d33 of 24 pC/N after annealing at 700°C. Moreover, the poled composite has displayed strong radial and thickness dielectric resonances at 20–700°C. Concluding the results, the CBN:40 wt%BFO composite with 0–3 type connectivity shows the stable high-temperature piezoelectric response much better than either CBN or BFO and is the worthier candidate to be utilized in high-temperature piezoelectric devices.

An appropriate amount of Zn-ions are incorporated into the high Curie temperature bismuth layer-structure ferroelectric material to fabricate Sr

Light-powered fuel-free colloidal motors possess significant potential for practical applications ranging from nanomedicine to environmental remediation. However, current light-powered colloidal motors often require the incorporation of expensive metals or high concentrations of toxic chemical fuels, which is a severe limitation for their practical applications. Integrating highly ordered and porous materials with a large surface area into colloidal motors is a promising strategy for upsurging their self-propelled speed and adsorption, which will benefit many applications. Here, highly efficient, fuel-free, and light-activated metal organic framework (MOF)-3-trimethoxysilyl propyl methacrylate Janus colloidal motors with a hierarchical morphology are reported. These colloidal motors can be driven by UV or visible light, with a self-propelled speed tuned by the light intensity. The speed can be further enhanced by morphology optimization or by the addition of H2O2 as a fuel. The colloidal motors display a superior efficiency in removing heavy metal ions of Hg, which is up to ∼90% within 40 min from the contaminated water, attributed to their high surface area, hierarchical morphology, large number of active sites, and high mobility. This work not only offers a facile approach to incorporate a versatile MOF family into the design of fuel-free and light-powered Janus colloidal motors, but also demonstrates their potential for real-life applications such as environmental remediation.

The current study describes the structural and magnetic properties of Ba0.9Sm0.1Fe12−x Al x O19 (x = 0.0, 0.5, 1.0, 2.0, 3.0) M-type hexaferrites. The conventional ceramic route was implied to prepare all the nominal samples. Morphological analysis suggested the non-presence of secondary phases as well as the formation of the hexaferrites material. X-ray Diffraction technique was used for structural analysis from which microstructural parameters are calculated and discussed. Magnetic properties are measured at room temperature. The saturation magnetization (Ms) and coercivity (Hc) values show a cyclic and converse trend for synthesized samples. Firstly, a decrease in Ms and an increase in Hc was observed up to intermediate dopant incorporation and becomes converse for higher doping levels. The maximum coercivity and minimum magnetization are observed for Ba0.9Sm0.1Fe11Al1O19. The c/a and Mr/Ms ratio suggest the formation of perfect M-type hexaferrites. This work suggests that synthesized material is a good option for magnetic applications e.g., transformer and inductor cores, microwave devices, recording heads, and magnetic shielding.

SnO

Morphotropic phased boundary (MPB) existent Bi0.5(K0.2Na0.8)0.5TiO3:xwt%MnO2 (BKNT:xMn) ceramic system is fabricated to investigate the ferroelectric and piezoelectric properties. All the ceramic samples have maintained the tetragonal (P4mm)-rhombohedral (R3c) structural duality due to MPB regional investigation of BKNT. The addition of MnO2 in BKNT has improved the multifunctional properties of the material at x ​= ​0.15. BKNT:0.15Mn ceramic has shown the maximum density of 6.98 ​g/cm3, remnant polarization (Pr) ​∼ ​32.5 ​μC/cm2, high impedance of ∼108 ​Ω, d33 of 206 ​pC/N, which are much improved properties than pure single phase BKNT and Bi0.5K0.5TiO3 ceramics. The dependence of dielectric constant (er) on temperature suggests the relaxor behavior and the high Curie temperature (TC) ​∼ ​410 ​°C for BKNT:0.15Mn ceramic, higher than the TC ​∼ ​360 ​°C of pure BKNT ceramic. The poled ceramics have maintained the stable piezoelectric properties till 300 ​°C. The introduction of multivalence Mn has improved the multifunctional properties of the material significantly, making it a strong candidate to be utilized in actuators and sensors.

Optoelectronic and thermoelectric properties of SrXO4 (X ​= ​S, Se, Te) have been investigated with the help of WIEN2K code by using FP-LAPW method and GGA approximation of the DFT approach. The obtained results show that SrSO4 and SrSeO4 are direct wide band gap semiconductors, while, SrTeO4 is an indirect band gap semiconductor. Based on theoretical study of optical properties, it has been established that the investigated compounds are promising candidates for active optical devices operating in the UV and visible range. These compounds have also been found to be weak reflectors for incident photons as they reflect up to 60% of the incident photons in the upper UV region. The semi-classical Boltzmann transport kinetic equations are used to study thermoelectric properties such as electrical conductivity, thermal conductivity, power factor, Seebeck coefficient and Figure of merit of the considered compounds. The research shows that SrSeO4 and SrTeO4 are promising compounds for thermoelectric devices.

Development of efficient, renewable and eco-friendly energy sources is on rise and is the main quest of the researchers to meet the energy challenges of future due to vanishing fossil fuels. In this connection, chalcogenides are the most promising materials to be used in state-of-the-art next generation solar cells for efficient production of clean energy from solar radiations. Hereby, we have presented an organized investigation of the optical and electronic properties of XCu3Se4 (X ​= ​Nb, Ta, V) by using first-principles GGA ​+ ​U calculations for their potential applications in optoelectronic devices such as solar cells. Our calculations show that NbCu3Se4 and TaCu3Se4 are semiconductor compounds; however, VCu3Se4 is intermetallic in nature because it shows semiconducting nature in the minority spin channel and metallic nature in the majority spin channel. NbCu3Se4 and TaCu3Se4 possess indirect band gaps as valence band maxima (VBM) and conduction band minima (CBM) are present at two different axes of IBZ (irreducible Brillouin zone), however, VCu3Se4 possess direct band gap in minority spin channel and shows metallic nature in majority spin channel. Energy band gaps of aforesaid compounds increase by replacing Nb with Ta and V. We have reported a detailed investigation of the optical constants to explore the prospect of these materials for optoelectronic applications. This study reveals that these compounds are weak reflectors of incident photons in infrared and visible regions, however, these compounds show up to 50% reflection of incident photons in the upper UV region. Elastic results reveal that these cubic compounds are elastically anisotropic materials with covalent bonding. Material shows ductile nature if value of (B/G) is greater than 1.75 otherwise it must be brittle. In our case, values of (B/G) or NbCu3Se4, TaCu3Se4 and VCu3Se4 are less than 1.75. Therefore, these chalcogenides are brittle in nature.

Silicides have been of great interest for thermoelectric applications due to their abundant elements as well as thermal and chemical stability. In this paper, we examined the thermoelectric properties of Yb3Si5 polycrystalline samples in a wide temperature range from 10 to 800 K. The temperature dependence of the Seebeck coefficient was successfully analyzed by assuming a narrow 4f quasi-particle band, indicating the intermediate valence state of Yb2+-Yb3+ is responsible for the high power factor. A very large maximum power factor of ∼ 4.70 mWm−1K−2 was observed at 72 K and room temperature value ∼ 1.56 mWm−1K−2 for Yb3Si5. These results shows that Yb-Si compounds have large potential to be used as low temperature TE applications in the future. We also studied the Co-doping effect in Yb3Si5, namely, Yb3Co x Si5−x where x = 0, 0.1, 0.15, 0.20 and investigated their thermoelectric properties. While powder X-ray diffraction analysis confirmed all main peaks indexed to Yb3Si5 phase, SEM and EDX analyses revealed that Co is precipitated as metal particles, forming a composite material with Yb3Si5 phase. Thermoelectric properties of the Co-doped samples are also reported.

Although the theoretical capacitance of MnO2 is 1370 F g–1 based on the Mn3+/Mn4+ redox couple, most of the reported capacitances in literature are far below the theoretical value even when the material goes to nanoscale. To understand this discrepancy, in this work, the electrochemical behavior and charge storage mechanism of K+-inserted α-MnO2 (or KxMnO2) nanorod arrays in broad potential windows are investigated. It is found that electrochemical behavior of KxMnO2 is highly dependent on the potential window. During cyclic voltammetry cycling in a broad potential window, K+ ions can be replaced by Na+ ions, which determines the pseudocapacitance of the electrode. The K+ or Na+ ions cannot be fully extracted when the upper cutoff potential is less than 1 V vs Ag/AgCl, which retards the release of full capacitance. As the cyclic voltammetry potential window is extended to 0–1.2 V, enhanced specific capacitance can be obtained with the emerging of new redox peaks. In contrast, the K+-free α-MnO2 nanorod ar...

Polyaniline (PANI), one of the most attractive conducting polymers for supercapacitors, demonstrates a great potential as high performance pseudocapacitor materials. However, the poor cycle life owing to structural instability remains as the major hurdle for its practical application; hence, making the structure-to-performance design on the PANI-based supercapacitors is highly desirable. In this work, unique core-shell NiCo2O4@PANI nanorod arrays (NRAs) are rationally designed and employed as the electrode material for supercapacitors. With highly porous NiCo2O4 as the conductive core and strain buffer support and nanoscale PANI layer as the electrochemically active component, such a heterostructure achieves favorably high capacitance while maintaining good cycling stability and rate capability. By adopting the optimally uniform and intimate coating of PANI, the fabricated electrode exhibits a high specific capacitance of 901 F g(-1) at 1 A g(-1) in 1 M H2SO4 electrolyte and outstanding capacitance retention of ∼91% after 3000 cycles at a high current density of 10 A g(-1), which is superior to the electrochemical performance of most reported PANI-based pseudocapacitors in literature. The enhanced electrochemical performance demonstrates the complementary contributions of both componential structures in the hybrid electrode design. Also, this work propels a new direction of utilizing porous matrix as the highly effective support for polymers toward efficient energy storage.

Binder-free and self-standing lithium titanate nanoarrays could be promising 3D anodes for lithium-ion microbatteries. The intrinsic poor electrical conductivity of Li4Ti5O12, however, spoils its rate performance and restrains its application in commercial batteries. In this work, black mesoporous Li4Ti5O12−δ nanowall arrays with oxygen vacancies are synthesized by a facile hydrothermal method with post heat treatment in an Ar atmosphere. The heat treatment in an inert atmosphere is effective for generating oxygen vacancies by forming Ti3+ ions in Li4Ti5O12−δ nanowall arrays, thus greatly enhancing the electron transfer in the spinel structure. Consequently, the black mesoporous Li4Ti5O12−δ nanowall arrays exhibit greatly improved electrode kinetics and rate performance compared to the stoichiometrical Li4Ti5O12 and Li4Ti5O12/TiO2 dual phase nanowall arrays. In specific, the black mesoporous Li4Ti5O12−δ nanowall arrays can deliver a large specific capacity of about 115 mA h g−1 at 20C as well as excellent cycling stability, making them promising as 3D anodes for advanced lithium-ion microbatteries.

SnO2/α-Fe2O3 hybrid nanofibers, consisting of one dimensional hollow SnO2 nanotubes decorated with Fe2O3 particles, are synthesized via a facile electrospinning process followed by a hydrothermal treatment and investigated as the anode material for lithium-ion batteries. The SnO2/Fe2O3 hybrid nanofibers not only provide a large surface area for lithium storage sites, but also show the capability of fast charge transport for both electrons and lithium ions. Both SnO2 and Fe2O3 contribute to the lithium storage and the hybrid structure exhibits a synergistic effect when participating in electrochemical reactions. With the smart structure design, the hybrid SnO2/Fe2O3 nanofiber electrode shows superior electrochemical performance compared to the bare SnO2 nanofiber electrode. In addition to a large first-cycle discharge capacity up to 1105 mAh g-1, the hybrid SnO2/Fe2O3 nanofibers electrode also exhibits good cycling stability and high rate capability.

The voltage limit for aqueous asymmetric supercapacitors is usually 2 V, which impedes further improvement in energy density. Here, high Na content Birnessite Na

Although the theoretical capacitance of MnO

The voltage limit for aqueous asymmetric supercapacitors is usually 2 V, which impedes further improvement in energy density. Here, high Na content Birnessite Na0.5 MnO2 nanosheet assembled nanowall arrays are in situ formed on carbon cloth via electrochemical oxidation. It is interesting to find that the electrode potential window for Na0.5 MnO2 nanowall arrays can be extended to 0-1.3 V (vs Ag/AgCl) with significantly increased specific capacitance up to 366 F g-1 . The extended potential window for the Na0.5 MnO2 electrode provides the opportunity to further increase the cell voltage of aqueous asymmetric supercapacitors beyond 2 V. To construct the asymmetric supercapacitor, carbon-coated Fe3 O4 nanorod arrays are synthesized as the anode and can stably work in a negative potential window of -1.3 to 0 V (vs Ag/AgCl). For the first time, a 2.6 V aqueous asymmetric supercapacitor is demonstrated by using Na0.5 MnO2 nanowall arrays as the cathode and carbon-coated Fe3 O4 nanorod arrays as the anode. In particular, the 2.6 V Na0.5 MnO2 //Fe3 O4 @C asymmetric supercapacitor exhibits a large energy density of up to 81 Wh kg-1 as well as excellent rate capability and cycle performance, outperforming previously reported MnO2 -based supercapacitors. This work provides new opportunities for developing high-voltage aqueous asymmetric supercapacitors with further increased energy density.