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The reliability of negative temperature coefficient (NTC) thermistors is one of the important factors for the excellent performance of the battery management system in electric vehicles. The electrical properties of the thermistor can be explained by the indirect electron jump between Mn3+ and Mn4+ at the B-sites in a spinel-type thermistor. Additionally, different types of dopants, such as Fe, Cu, Zn, Cr, and Mn, are considered as electrical modifiers that can further improve the electrical properties of the thermistor. For example, Cu is often added to NTC thermistors, occupying the octahedral sites in a spinel-type thermistor, which can play an important role in conduction with the Mn cations. Addition of Fe is also widely used in NTC thermistors owing to its high sensitivity, B constant, and stability. In this study, composition-dependent structural and electrical properties of Cu0.2/Fey-co-doped Ni0.3Mna-x-yCo0.9O4 (NMC) are investigated. Cu/Fe-co-doped NMC shows the R25 and B25/85 constant values of 4490–12730 Ω and 3185–3490 K, respectively, exhibiting a typical ρ–T curve of NTC thermistors. Higher B constant and reliable electrical stability are observed for Cu/Fe-co-doped NMC. Based on the relationship between the cationic oxidation states and electrical properties of Cu/Fe-co-doped NMC, the hopping conduction mechanism is discussed.

Diabetes is a chronic disease, which can give serious damages to the human organs that affect life expectancy. Such a life-threatening diabetes is diagnosed by systematic monitoring of blood glucose levels; thus, accurate detection of glucose within a specified target range becomes more important for glucose sensor to provide detailed information relating with diabetes, which can result in reliable decision for diabetes treatment. Thanks to many efforts developing the reliable glucose sensors, electrochemical performance of the sensor including sensitivity and selectivity in response to glucose is gradually improved. Herein, we developed spinel type NiCo2O4 (NCO) nanostructure with excellent sensitivity, selectivity and chemical robustness for glucose detection. NCO was prepared by conversion of NiCo-layered double hydroxide (NCH) at comparatively low temperature, which is synthesized by simple and facile chemical bath method and following post-heat treatment of the NCH. Electrochemical sensitivity, selectivity and detection time of the NCO in response to glucose was investigated, compared to those of the NCH. Also, long-term stability of the NCO on repetitive glucose detection was evaluated. Based on the systematic analysis on materials properties and electrochemical performance of the NCO, possible mechanism of the glucose oxidation, which significantly improves electrochemical performance of the NCO, is discussed.

Crystal structures and hopping motions of cobalt manganese spinel oxides across a wide composition range (CoxMn3−xO4 (CMO), 0.9 ≤ x ≤ 2.7) are investigated in order to clarify the corresponding mechanisms of electrical behaviors as negative temperature coefficient thermistors. Based on the diffraction measurements, a tetragonal to cubic spinel transition are observed mostly with increasing Co content. Hopping distance for a series of CMO are calculated by the variable range hopping mechanism, which is changed as a function of composition, resulting to the observed unique electrical properties. According to the electrical and structural analysis, the electrical properties of CMO compounds with different Co contents majorly determined by tetragonal to cubic phase transition, cation distribution, and hopping distance. In addition, the formation of secondary phase (i.e., CoO) and another CMO phase may also significantly affect the electrical properties.

Phase evolution of (Ni, Co, Mn)O 4 (NMC) for negative thermal coefficient (NTC) thermistor is investigated using high temperature X-ray diffraction. Diffraction patterns were collected during heating and cooling, allowing the observation of chemical reactions in the range of temperature between 25 and 1400 °C. NiO, Mn 3 O 4 and CO 3 O 4 as the reactant materials were prepared using spray drying. As increasing temperature, phase transformation of Mn 3 O 4 to Mn 2 O 3 was first observed prior to the formation of NMC spinel structure at 700 °C. Between 1000 and 1200 °C, only spinel NMC was observed without any other phases. Also, grain growth of NMC was observed. Phase transition from cubic to tetragonal was observed during cooling. With further increasing temperature up to 1400 °C, thermal stability of NMC decrease, which was confirmed by NiO separation due to the thermal decomposition. Thermogravimetric and differential thermal analysis are performed on NMC compound and the results support the mechanism of phase formation presented by high temperature XRD data. Also, electrical resistance of NMC is measured as a function of temperature (−40–80 °C) and the factor of thermal sensitivity ( B value) is calculated.

BDTI (backside deep trench isolation) structures parallel to a depth direction of a Si wafer may generate a stress concentration under the warpage caused by a mechanical loading on the wafer during handling or moving. Our work aims to provide a better understanding for minimizing a stress concentration effectively at the BDTI. To address shape factors of the BDTIs with a void, we change ? (open width), dBDTI (distance between Si-surface and BDTI bottom), ? (angle between Si-surface and sidewall of BDTI), and t1st HfOx (thickness of 1st HfOx film on silicon surface). Among the geometrical factors changed in this work, our simulation predicts that the opening length and the thickness of 1st HfOx films are key factors to control a maximum stress concentration at a 1st HfOx film below an oxide bottom. Comparing only a final geometry of various BDTIs, it is consequently very effective to decrease the interface curvature between an HfOx and oxide films in order to get low stress structures.

Transition metal layered double hydroxides (LDHs) have received much attention as high-performance oxygen evolution reaction (OER) catalysts due to their large number of active sites with favorable adsorption/desorption energies for intermittent reactants. However, the relatively sluggish charge transfer kinetics of transition metal LDHs due to their intrinsically low conductivity often hinders their use in practical applications as high-performance water oxidation catalysts. Here, we disclose a novel strategy of metalloid incorporation into transition metal LDHs, allowing us to simultaneously optimize surface electronic configuration and charge transfer between adsorbed reactants and catalyst surface. Importantly, incorporated metalloid can enhance the density of states (DOS) near the Fermi level and alter the nature of the chemical bonds in the catalytically active atoms, resulting in fast reaction kinetics. Thus, metalloid incorporation into transition metal LDHs can substantially improve the overall reaction kinetics and thermodynamics for water oxidation due to a large number of active sites and high conductivity, boosting OER performance of transition metal LDHs. The metalloid-incorporated transition metal LDHs far outperform their counterpart transition metal LDHs and even the noble metal catalyst RuO2.

The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon‐based functional materials. However, a fundamental deep understanding of the formation of graphene quantum dots (GQDs) from multiwalled carbon nanotubes (MWCNTs) by PLFL has still not been achieved despite the high demand. In article number 2003538, Jeong Ho Ryu, Hyuksu Han, Kang Min Kim, and co‐workers report a mechanism for the formation of GQDs from MWCNTs by the PLFL process, through the combination of experimental and theoretical studies.

The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon-based functional materials. In particular, there has been considerable attention on graphene quantum dots (GQDs) derived from multiwalled carbon nanotubes (MWCNTs) by the PLFL process, owing to the low cost and rapid processing time involved. However, a fundamental deep understanding of the formation of GQDs from MWCNTs by PLFL has still not been achieved despite the high demand. In this work, a mechanism for the formation of GQDs from MWCNTs by the PLFL process is reported, through the combination of experimental and theoretical studies. Both the experimental and computational results demonstrate that the formation of GQDs strongly depends on the pulse laser energy. Both methods demonstrate that the critical energy point, where a plasma plume is generated on the surface of the MWCNTs, should be precisely maintained to produce GQDs; otherwise, an amorphous carbon structure is favorably formed from the scattered carbons.

Development of a cost-effective oxygen evolution reaction (OER) catalyst for hydrogen production from water has attracted the attention of scientists due to its potential to solve current environmental and energy issues, such as CO2 emissions and depletion of fossil fuels. In this paper, we report a facile synthesis to develop cobalt-manganese-oxide (MnxCo3−xO4, CMO) nanorods via an oxalate precipitation method followed by annealing at different temperatures. Importantly, morphology and surface area of the CMO nanorods, which are directly related to the OER activity, can be precisely controlled by changing annealing temperatures. The CMO nanorods engineered by oxalate precipitation and subsequent heat treatment show promising OER catalytic performance, such as a small overpotential of 365 mV for generating a current density of 10 mA cm−2, a low Tafel slope of 50.6 mV dec−1, and excellent long-term stability in alkaline media. Electrochemical properties combined with materials characterization provide insightful information on the OER mechanism of the CMO nanorods.

A novel Ce3+-doped Lu3MgAl3SiO12 (LCMAS) phosphor was successfully synthesized by a conventional solid-state reaction. The crystal structure of the LCMAS was characterized by Rietveld refinement. The broad emission spectra of the LCMAS were observed at 550 nm, and the temperature dependence on photoluminescence properties of the LCMAS was investigated. Also, the activation energy for thermal quenching was determined by Arrhenius fitting. The experimental results clearly indicate that the LCMAS phosphor has a great potential for the down-conversion of yellow phosphor into white light-emitting diodes.

Lead-free piezoelectric materials have been actively studied to substitute for conventional PZT based solid solution, , which occurs unavoidable PbO during the sintering process. Among them, Bismuth Sodium Titanate, (abbreviated as NBT) based solid solution is attracted for the one of excellent candidates which shows the strong ferroelectricity, Curie temperature (Tc), remnant polarization (Pr) and coercive field (Ec). Especially, the solid solution of rhombohedral phase NBT with tetragonal perovskite phase has a rhombohedral - tetragonal morphotropic phase boundary. Modified NBT with tetragonal perovskite at the region of MPB can be applied for high frequency ultrasonic application because of not only its low permittivity, high electrocoupling factor and high mechanical strength, but also effective piezoelectric activity by poling. In this study, solid state ceramic processing of NBT and modified NBT, (abbreviated as NBT-7BT), at the region of MPB using 7 % as a tetragonal perovskite was introduced and the structure between NBT and NBT-7BT were analyzed using rietveld refinement. Also, the ferroelectric and piezoelectric properties of NBT-7BT such as permittivity, piezoelectric constant, polarization hysteresis and strain hysteresis loop were compared with those of pure NBT.

Titanium dioxide (TiO

The crystallization of lead zirconate titanate (PZT) thin films was evaluated on two different platinum-coated Si substrates. One substrate consisted of a Pt coating on a Ti adhesion layer, whereas the other consisted of a Pt coating on a TiO2 adhesion layer. The Pt deposited on TiO2 exhibited a higher degree of preferred orientation than the Pt deposited on Ti (as measured by the Full Width at Half Maximum of the 111 peak about the sample normal). PZT thin films with a nominal Zr/Ti ratio of 52/48 were deposited on the substrates using the inverted mixing order (IMO) route. Phase and texture evolution of the thin films were monitored during crystallization using in situ X-ray diffraction at a synchrotron source. The intensity of the Pt3Pb phase indicated that deposition on a highly oriented Pt/TiO2 substrate resulted in less diffusion of Pb into the substrate relative to films deposited on Pt/Ti. There was also no evidence of the pyrochlore phase influencing texture evolution. The results suggest that PZT nucleates directly on Pt, which explains the observation of a more highly oriented 111 texture of PZT on the Pt/TiO2 substrate than on the Pt/Ti substrate.

Graphene quantum dots (GQDs) have attractive properties and potential applications. However, their various applications are limited by a current synthetic method which requires long processing time. Here, we report a facile and remarkably rapid method for production of GQDs exhibiting excellent optoelectronic properties. We employed the pulsed laser ablation (PLA) technique to exfoliate GQDs from multi-wall carbon nanotube (MWCNTs), which can be referred to as a pulsed laser exfoliation (PLE) process. Strikingly, it takes only 6 min to transform all MWCNTs precursors to GQDs by using PLE process. Furthermore, we could selectively produce either GQDs or graphene oxide quantum dots (GOQDs) by simply changing the organic solvents utilized in the PLE processing. The synthesized GQDs show distinct blue photoluminescence (PL) with excellent quantum yield (QY) up to 12% as well as sufficient brightness and resolution to be suitable for optoelectronic applications. We believe that the PLE process proposed in this work will further open up new routes for the preparation of different optoelectronic nanomaterials.

High-performance oxygen evolution reaction (OER) electrocatalysts are needed to produce hydrogen for energy generation through a carbon-free route. In this work, the solution combustion synthesis (SCS) method was employed to synthesize mixed phases of Co- and Mn-based oxides, and the relationships between the crystalline structure and the catalytic properties in the mixed phases were established. The mixed phases of Co- and Mn-based oxides shows promising OER properties, such as acceptable overpotential (450 mV for 10 mA∙cm&minus, 2) and Tafel slope (35.8 mV∙dec&minus, 1), highlighting the use of the mixed phases of Co- and Mn-based oxides as a new efficient catalysts for water splitting. Electronic structure of the mixed phases of Co- and Mn based oxides is studied in detail to give insight for the origin of high catalytic activities. In addition, excellent long-term stability for OER in alkaline media is achieved for the mixed phase of Co- and Mn based oxides.

The crystallization behavior of solution-derived lead zirconate titanate (PZT) thin films in different atmospheric environments was studied using in situ X-ray diffraction. The stability of the transient intermetallic Pt3Pb phase and perovskite PZT is dependent on oxygen partial pressure during crystallization. Based on the relationship between oxygen partial pressure and the resultant phase stability of intermediate phases, a new route to produce PZT thin films was developed. The new route involves switching atmospheres during crystallization and is shown to mitigate the formation of the transient intermetallic Pt3Pb phase and to promote the perovskite PZT phase. The route evidences a new and significant variable controlling film synthesis and film microstructure.

International audience; Hopping motions in cobalt manganese spinel oxides with high cobalt concentration (CoxMn3−xO4, 2.3 ≤ x ≤ 2.7) are investigated in order to clarify the origin of unusual electrical behaviors as negative temperature coefficient (NTC) thermistors. Based on the resistance versus temperature (R−T) characteristics, hopping conduction mechanisms in MCO compounds (x = 2.3 and 2.5) are attributed to variable range hopping (VRH) motion with a parabolic distribution of the density of states (DOS) near the Fermi level. However, when Co content increases up to 2.7, transition in the hopping motion occurs from VRH to the nearest neighboring hopping (NNH) motion, which can be responsible for a huge increase of the resistance accompanied by decrease of the factor of thermal sensitivity (B value) in MCO compounds (x = 2.7). Also, hopping distance and activation energies for MCO (x = 2.3 and 2.5) compounds following VRH conduction are calculated as a function of temperature, indicating that higher B value observed in MCO (x = 2.5) compound is due to the larger hopping distance compared to that of MCO (x = 2.3) compound.

Pulsed laser ablation (PLA) in liquid medium was successfully employed to synthesize hydroxyapatite (HAp) colloidal nanoparticles. The crystalline phase, particle morphology, size distribution and microstructure of the HAp nanoparticles were investigated in detail. The obtained HAp nanoparticles had spherical shape with sizes ranging from 5 to 20 nm. The laser ablation and the nanoparticle forming process were studied in terms of the explosive ejection mechanism by investigating the change of the surface morphology on target. The stoichiometry and bonding properties were studied by using XPS, FT-IR and Raman spectroscopy. A molar ratio of Ca/P of the prepared HAp nanoparticles was more stoichiometric than the value reported in the case of ablation in vacuum.

Pulsed laser ablation in a liquid phase was successfully employed to synthesize a barium molybdate (BaMoO4) nanocolloidal suspension. The nanocolloidal suspension was composed of well-dispersed and horizontally assembled BaMoO4 aggregates. The BaMoO4 aggregates showed predominantly elliptically shaped nanorods with sizes between 100 and 200 nm. The preferential elliptical growth was rationalized from the viewpoint of the intrinsic structure of BaMoO4. The optical properties of the prepared BaMoO4 colloidal nanoparticles were investigated using Raman spectroscopy, UV–vis spectroscopy and photoluminescence (PL) spectrophotometry. The optical band gap was estimated by Tauc and Menth’s law. The PL emission feature was decomposed into several individual Gaussian components, which could be interpreted by a Jahn–Teller splitting effect on the [MoO4]2- tetrahedron of the BaMoO4 colloidal nanoparticles.

Epitaxial Ba2FeMoO6 thin films were grown via pulsed laser deposition under low oxygen pressure and their structural, chemical, and magnetic properties were examined, focusing on the effects of oxygen pressure. The chemical disorder, off-stoichiometry in B site cations (Fe and Mo) increased with increasing oxygen pressure and thus magnetic properties were degraded. Interestingly, in contrast, negative magneto-resistance, which is the characteristics of this double perovskite material, was enhanced with increasing oxygen pressure. It is believed that phase segregation of highly disordered thin films is responsible for the increased magneto-resistance of thin films grown at high oxygen pressure. The anomalous Hall effect, which behaves hole-like, was also observed due to spin-polarized itinerant electrons under low magnetic field below 1 T and the ordinary electron-like Hall effect was dominant at higher magnetic fields.

The authors report a novel synthetic route for Ho3+/Yb3+ codoped calcium molybdate (CaMoO4) nanoparticles by pulsed laser ablation in ethanol. Well-dispersed Ho3+/Yb3+ codoped CaMoO4 nanocolloid was prepared without any surfactant. Crystallographic information, microstructure, and the upconversion (UC) luminescent properties of the nanocolloid were investigated. Under the excitation at 980 nm, Ho3+/Yb3+ codoped CaMoO4 nanocolloid exhibited strong yellow emission visible to the naked eyes, which is the combination of green emission near 542 nm and strong red emission around 656 nm. Based on the pump power dependence, UC mechanism of Ho3+/Yb3+ codoped CaMoO4 nanocolloid was discussed in detail.

Understanding interfaces between dissimilar materials is crucial to the development of modern technologies, for example, semiconductor–dielectric and thermoelectric–semiconductor interfaces in emerging electronic devices. However, the structural characterization of buried interfaces is challenging because many measurement techniques are surface sensitive by design. When interested in interface evolution during synthesis, the experimental challenges multiply and often necessitate in situ techniques. For solution-derived lead zirconate titanate (PZT) ferroelectric thin films, the evolution of buried interfaces during synthesis (including dielectric–metal and metal–metal) is thought to dramatically influence the resultant dielectric and ferroelectric properties. In the present work, multiple experimental and computational methods are combined to characterize interface evolution during synthesis of ferroelectric PZT films on platinized Si wafers—including in situ X-ray diffraction during thermal treatment, aberration-corrected scanning transmission electron microscopy of samples quenched from various synthesis states, and calculations using density functional theory. Substantial interactions at buried interfaces in the PZT/Pt/Ti/SiO x /Si heterostructure are observed and discussed relative to their role(s) in the synthesis process. The results prove that perovskite PZT nucleates directly from the platinum (111)-oriented bottom electrode and reveal the roles of Pb and O diffusion and intermetallic Pt3Pb and Pt3Ti phases.

An in situ measurement technique is developed and presented, which utilizes x-rays from a synchrotron source with a two-dimensional detector to measure thin film microstructural and crystallographic evolution during heating. A demonstration experiment is also shown wherein the measured diffraction patterns are used to describe phase and texture evolution during heating and crystallization of solution-derived thin films. The diffraction images are measured sequentially while heating the thin film with an infrared lamp. Data reduction methodologies and representations are also outlined to extract phase and texture information from the diffraction images as a function of time and temperature. These techniques and data reduction methods are demonstrated during crystallization of solution-derived lead zirconate titanate ferroelectric thin films heated at a rate of 30 °C/min and using an acquisition time of 8 s. During heating and crystallization, a PtxPb type phase was not observed. A pyrochlore phase was obse...

Phase pure Ba2FeMoO6 thin films were grown by pulsed laser deposition at substrate temperatures ranging from 600 to 900 °C, and the structural, magnetic, and magnetotransport properties were investigated. The grain size, the conductivity, the saturation magnetization, and the coercive field all increase with increasing growth temperature, while the Curie temperature remains relatively constant. All samples showed negative magnetoresistance which is consistent with the half metallic property of double perovskites. Interestingly, the samples grown on the higher temperature substrates showed a small low-field positive magnetoresistance which is not understood. We also have observed an anomalous Hall effect, due to spin-polarized itinerant electrons, in which the saturation field of the hole-like anomalous portion decreases with increasing temperature and at higher temperatures manifests a negative slope (ordinary Hall effect) indicative of negative charge carriers.

The polycrystalline Ho3+/Tm3+/Yb3+ co-doped CaMoO4 phosphors were successfully synthesized by complex citrate-gel method. Under the laser excitation of 980 nm, Ho3+/Tm3+/Yb3+ co-doped CaMoO4 shows the bright white upconversion (UC) emission visible to the naked eye, which is composed of a blue emission at 475 nm from Tm3+, and green and red emissions at 543 nm and 651 nm from Ho3+. The coordinates of Ho3+/Tm3+/Yb3+ co-doped CaMoO4 in the commission international de'eclairage (CIE) chromaticity diagram can be controlled from a cool to a warm white color depending on the Tm3+ and Ho3+ concentrations. In Ho3+/Tm3+/Yb3+ co-doped CaMoO4, the UC luminescent properties on Tm3+ and Ho3+ concentrations and mechanism based on laser pump power were discussed in detail.

Ce 3+ -doped nanocrystalline terbium aluminum garnet (Tb 3 Al 5 O 12 :Ce 3+ , TAG:Ce 3+ ) phosphors were successfully synthesized in low temperature by nitrate-citrate gel combustion method using microwave irradiation as a heating source. The pure TAG phase was obtained after calcining at 800°C for 6 h. The prepared nanocrystalline phosphors showed a broad peak at 551 nm, and the maximum doping concentration of Ce 3+ for the highest emission intensity was 0.8 mol % at 551 nm. The temperature dependence on photoluminescence properties of the prepared TAG:Ce 3+ phosphors was investigated from 25 to 275°C, and the activation energies (ΔE) for thermal quenching was determined by Arrhenius fitting. The experimental results clearly indicate that prepared nanocryatalline TAG: Ce 3+ has great potentials for a down-conversion yellow phosphor in white light emitting diodes.

Pulsed laser ablation in deionized water was successfully employed to synthesize a Y 3 Al 5 O 12 :Ce 3+ nanocolloidal suspension. The obtained suspension consisted of a well-dispersed YAG:Ce 3+ nanocrystal with a spherical shape and a size ranging from 5 to 25 nm. Blueshift phenomena were found in excitation and emission spectra, which have not been explained by previous crystal-field splitting theory. This Letter focuses on the simple synthetic route of colloidal YAG:Ce 3+ nanocrystals via laser ablation in the liquid phase and 5d energy level of Ce 3+ . A phenomenological model based on the concept of crystal-field theory modified by the covalency contribution is introduced to explain the blueshift phenomena in luminescence.

Cerium-doped Tb3Al5O12(TAG:Ce3+) colloidal nanocrystals were synthesized by pulsed laser ablation (PLA) in de-ionized water and lauryl dimethylaminoacetic acid betain (LDA) aqueous solution for luminescent bio-labeling application. The influence of LDA molecules on the crystallinity, crystal morphology, crystallite size, and luminescent properties of the prepared TAG:Ce3+colloidal nanocrystals was investigated in detail. When the LDA solution was used, smaller average crystallite size, narrower size distribution, and enhanced luminescence were observed. These characteristics were explained by the effective role of occupying the oxygen defects on the surface of TAG:Ce3+colloidal nanocrystal because the amphoteric LDA molecules were attached by positively charged TAG:Ce3+colloidal nanocrystals. The blue-shifted phenomena found in luminescent spectra of the TAG:Ce3+colloidal nanocrystals could not be explained by previous crystal field theory. We discuss the 5d energy level of Ce3+with decreased crystal size with a phenomenological model that explains the relationship between bond distance with 5d energy level of Ce3+based on the concept of crystal field theory modified by covalency contribution.