Functional Materials Letters

Microbatteries are currently the best choice to power microelecronic devices. To maximize both energy density and power density of microbatteries within the areal footprint, the three-dimensional (3D) microbattery architectures have been proposed, comprising a 3D matrix of components (cathode, anode and electrolyte) arranged in either a periodic array or an aperiodic ensemble. As one of the key components, the cathode is vital to the electrochemical performance of microbatteries and the fabrication of 3D cathode is still challenging. This review describes recent advances in the development of 3D self-supported metal oxides as cathodes for lithium-ion microbatteries. Current technologies for the design and morphology control of 3D cathode fabricated using template, laser structuring and 3D printing are outlined along with different efforts to improve the energy and power densities.

Three sets of Sn–Co alloy films were electrochemically deposited onto nodule-type Cu foil in aqueous solution. The results of X-ray diffraction (XRD), atomic absorption spectroscopy (AAS) and scanning electron microscopy (SEM) proved that the electrochemical current density and the depositing time had influence on the structure and the morphology of the alloy films. The electrochemical properties of the Sn–Co alloy film electrodes for lithium-ion battery were investigated by galvanostatic charge-discharge test and cyclic voltammetry (CV). The Sn–Co alloy with the thickness of 0.8 μm created at the current density of 15 mA cm^-2 presents excellent electrochemical performance with the discharge capacity of 949.3 mAh g^-1 at the first cycle and 661.1 mAh g^-1 after 70 cycles. The high coulombic efficiency of almost 100% can be observed at different current rate. The improved performance is attributed to the structure of Cu foil, the optimized Co content and thickness of the alloy film, which were beneficial to strengthen the adhesion of the active materials to the current collector, shorten diffusion length of lithium ions and reduce the electrical resistance.

The purpose of this research is to study the effect of Se doping content on the improvement in thermoelectric properties of Bi₂Te_3-xSe_x bulk materials produced by high-pressure role. The Bi₂Te_3-xSe_x bulk materials can be successfully synthesized within 30 min due to high-pressure role, which significantly shortened the synthesis time. The typical textures of the reaction products exhibit abundant cracked crystal planes and special layer structures with increasing Se content, which can coordinate electrical and thermal transport in the Bi₂Te_3-xSe_x samples to achieve an optimal thermoelectric performance. As a result, a Bi₂Te_2.73Se_0.27 bulk material obtained a maximum ZT value of 1.03 at 344 K. These results suggest that the low Se doping content with high-pressure can improve the figure of merit of Bi₂Te_3-xSe_x materials.

La-modified ZnO nanosheet-assembled flower-like microstructures, were successfully obtained through a facile two-step solution-based strategy including a simple aqueous solution and subsequent impregnation technique. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and ultraviolet-visible spectrometer (UV-Vis) were employed to characterize the morphology, composition, crystal structure and photocatalytic properties of prepared products in detail. The photocatalysis test results revealed that the La-modified ZnO nanoflowers displayed greatly enhanced catalytic performance and the decomposition efficiency was up to about 99.60%, which was mainly ascribed to the increased charge separation rate on the La-modified surface of ZnO nanosheets and the high surface area of the flower-like structure.

The colorful BCNO phosphors comprised of boron, carbon, nitrogen, and oxygen atoms have been novelty synthesized by varying the environmental oxygen pressure without changing the compositions of the raw materials such as boric, urea, and poly-ethylene glycol. X-ray diffraction (XRD), fourier-transformed infrared (FTIR), and photoluminescence (PL) spectra were employed to characterize the effect of environmental oxygen pressure on the structure and PL properties of the synthesized phosphors. The results of their PL properties indicates that the emission color of these BCNO phosphors has been easily tailored for a large-range from violet to near-red regions through variations of the environmental oxygen pressure as prepared under the excitation of 365 nm. This provides a new approach to tailor the emitting colors.

We have observed the enhancement in photoluminescence (PL) intensity of the antiferroelectric liquid crystals (AFLC) doped with Sodium titanate nanoparticles (NPs). The enhancement in PL intensity of AFLC strongly depends on the doping concentration of NPs. The Sodium titanate NPs were prepared such that the emission from NPs together with AFLC molecules gives enhanced PL intensity. On the other hand, smectic C_A^* phase of AFLC provides strong light scattering and hence incident photons get scattered to excite more NPs and give enhanced PL counts. We have also observed the shift in emission energy band of AFLC doped with NPs.

In this paper, a gradient mesoporous carbon (GMC) monolith derived from the mixtures of phenolic resin (PF) and ethylene glycol (EG) was prepared by a facile route based on polymerization-induced phase separation under temperature gradient (TG). A graded biphasic structure of PF-rich and EG-rich phases was first formed in preform under a TG, and then the preform was pyrolyzed to obtain the GMC monolith. The TG is mainly induced by the thermal resistance of the preferential phase separation layer at high temperature region. The pore structure of the monolith changes gradually along the TG direction. When the TG varies from 58°C to 29°C, the pore size, apparent porosity and specific surface area of the monolith range respectively from 18 nm to 83 nm, from 32% to 39% and from 140.5 m²/g to 515.3 m²/g. The gradient porous structure of the monolith is inherited from that of the preform, which depends on phase separation under TG in the resin mixtures. The pyrolysis mainly brings about the contraction of the pore size and wall thickness as well as the transformation of polymerized PF into glassy carbon.

A facile and novel bubbling-assisted exfoliating method was developed for the preparation of γ-Fe₂O₃/graphene composite, which showed desirable photocatalytic activity toward methyl orange with excellent cycling abilities and the possible growth mechanism was discussed. Photocatalytic and magnetic properties measurements show that the composite has excellent recyclable degradation efficiency and soft magnetic parameters, which makes the composite magnetically separable in a suspension system and can be recycled without significant loss of catalytic activity.

Multiwalled carbon nanotubes (MWCNTs) were chemically split and self-assembled to a flexible porous paper made of graphene oxide nanoribbons (GONRs). The morphology and microstructure of the pristine MWCNTs and GONRs were analyzed by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy. And the specific surface area and porosity structure were measured by N₂ adsorption-desorption. The longitudinally split MWCNTs show an enhancement in specific capacitance from 21 F g^-1 to 156 F g^-1 compared with the pristine counterpart at 0.1 A g^-1 in a 6 M KOH aqueous electrolytes. The electrochemical experiments prove that the chemical splitting of MWCNTs will make inner carbon layers opened and exposed to electrochemical double layers, which can effectively improve the electrochemical capacitance for supercapacitors.

Epitaxial PbZr_0.52Ti_0.48O₃ (PZT) films with perfectly c-axis oriented tetragonal phase were deposited on SrTiO₃ (STO) substrates using a SrRuO₃ (SRO) buffer layer by pulsed laser deposition (PLD) method. Ferroelectric behavior of PZT on STO substrates along with an improved remnant polarization (2P_r) of 118 μC/cm² and a low coercive field (E_c) of 193 kV/cm at 15 V were observed at room temperature indicating that the SRO/STO substrates with small lattice misfit can make some contributions to enhance PZT film's ferroelectric properties. Moreover, the capacitance characteristics of the PZT thin films were detected, a large dielectric constant of 1476, the charging and discharging characteristics determine the large dielectric strength of the PZT thin film capacitors.

Partial oxalate route is an efficient method to synthesize complex perovskite ferroelectric ceramics, in which the synthesized (1 - x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ (PMN–PT) ceramics exhibit rather pure perovskite structure, densified microstructure morphology, and excellent dielectric and piezoelectric properties. The PMN–PT ceramics synthesized by the partial oxalate route exhibit rather symmetric strain–electric (S–E) field hysteresis loops, where the strain is large and far less than saturated at 2 kV/mm. The PMN–PT ceramics exhibit excellent pyroelectric properties, in which the values of the pyroelectric coefficient and the calculated pyroelectric figures of merit maintain almost stable over the frequency range of 100 Hz–2000 Hz, and vary differently depending on composition with the increase of temperature. Such investigations reveal that high-performance piezoelectric and pyroelectric devices can be prepared by the partial oxalate route in low production cost.

Europium-doped Na_1.45La_8.55-8.55x(SiO₄)₆(F_0.9O_1.1)(0.000 ≤ x ≤ 0.045) phosphors were prepared by a conventional solid-state reaction method at 1200°C and their properties were studied by X-ray diffraction (XRD), and a spectral analysis system. No impurities were observed. The phosphor could be excited at 254 nm, 395 nm and 465 nm to yield a reddish orange emission which was attributed to the ⁵D₀ → ⁷F_j (j = 0–2) transitions of the Eu ion.

Pure Li_1.1Ni_0.35Co_0.35Mn_0.30O₂ nanosized powders have been successfully synthesized by improved hydroxide co-precipitation method, and characterized with X-ray powder diffraction and scanning electron microscopy (SEM). The electrochemical properties of cathodes and Li_1.1Ni_0.35Co_0.35Mn_0.30O₂/Li₄Ti₅O₁₂ full cells have been studied by charge–discharge tests and cyclic voltammetry. The Li_1.1Ni_0.35Co_0.35Mn_0.30O₂ powders have a typical layered hexagonal crystal structure with an average particle size of about 780 nm. The cathodes exhibit high capacities and good cycling performance. The initial discharge capacity of the cathodes is 154.8 mAhg^-1 at 0.5 C between 2.5 V and 4.3 V, and the capacity retention keeps 80.6% after 50 charge–discharge cycles. The Li_1.1Ni_0.35Co_0.35Mn_0.30O₂/Li₄Ti₅O₁₂ cells also deliver high specific capacities, good cycling stability and rate capability. This work demonstrates that Li_1.1Ni_0.35Co_0.35Mn_0.30O₂ is a promising cathode material for lithium-ion batteries.

Functionalized copolymers of poly(aniline-co-o-iodoaniline) have been synthesized by the chemical oxidative polymerization method by using o-iodoaniline (o-IA) and aniline (AN) as monomer units by changing their molar feed ratio in acid aqueous medium. The physical properties viz; solubility, electrical conductivity have been studied to characterize them. The copolymers possess better solubility than unsubstituted homopolymer in organic solvent such as N-methyl-2-pyrrodinone (NMP). The conductivity of the pressed pellets of as-synthesized copolymers depends upon the content of o-IA in the polyaniline (PANI). The structural confirmation of the copolymer has been explained by Fourier transform infrared spectroscopy study which suggest that AN and o-IA units are uniformly distributed along the polymer chain and thus, the physical properties of copolymers may possibly be tailored by varying the molar feed ratio in copolymerization reactions. The conductivity of the copolymer decreases upon increasing the o-IA content in molar feed, because the introduction of –I^- as a functional group reduces the extent of conjugation of the polymer chain.

In this research, the high performance shape memory effect (HP-SME) is experimented on a shape memory NiTi wire, with austenite finish temperature higher than room temperature. The HP-SME consists in the thermal cycling of stress induced martensite and it allows achieving mechanical work higher than that produced by conventional shape memory actuators based on the heating/cooling of detwinned martensite. The Nitinol wire was able to recover about 5.5% of deformation under a stress of 600 MPa and to withstand about 5000 cycles before failure. HP-SME path increased the operating temperature of the shape memory actuator wire. Functioning temperatures higher than 100°C was reached.

TiO₂ nanobelts have been fabricated through a hydrothermal method and subsequently sulfuric-acid-corrosion-treated for a rough surface. Noble metal nanoparticles such as Ag and Au were deposited on the coarse surface of TiO₂ nanobelts via a coprecipitation procedure. Ag–TiO₂ nanobelts were prepared in ethanolic solution contained silver nitrate (AgNO₃) and sodium hydroxide (NaOH). Au–TiO₂ nanobelts were obtained in chloroauric acid (HAuCl₄) using sodium borohydride (NaBH₄) as the reductant. It is confirmed by the results of XRD patterns together with the SEM images that the composite of noble metal and TiO₂ nanobelts were obtained successfully and the Ag or Au nanoparticles were well-dispersed on the TiO₂ nanobelts. Moreover, the as-prepared Ag and Au nanoparticle-decorated TiO₂ nanobelts represent an enhanced photocatalytic activity compared with pure TiO₂ nanobelts, which is due to the fact that the Ag and Au nanoparticles on the surface of TiO₂ nanobelts act as sinks for the photogenerated electrons and promote the separation of the electrons and holes.