Enhanced thermal stability by short-range ordered ferroelectricity in K0.5Na0.5NbO3-based piezoelectric oxides.

Industrial application of lead-free piezoelectric ceramics is prevented by intrinsic thermal instability. Herein, we propose a method to achieve outstanding thermal stability of converse piezoelectric constant () in lead-free potassium sodium niobate (KNN)-based ceramics by inducing a synergistic interaction between the grain size and polar configuration. Based on computational methods using phase-field simulations and first-principles calculations, the relationship between the grain size and polar configuration is demonstrated, and the possibility of achieving improved thermal stability in fine grains is suggested. A set of KNN systems is presented with meticulous dopant control near the chemical composition at which the grain size changes abnormally. Comparing the two representative samples with coarse and fine grains, significant enhancement in the thermal stability of is exhibited up to 300 °C in the fine grains. The origin of the thermal superiority in fine-grained ceramics is identified through an extensive study from a microstructural perspective. The thermal stability is realized in a device by successfully demonstrating the temperature dependence of piezoelectricity. It is notable that this is the first time that lead-free piezoelectric ceramics are able to achieve exceptionally stable piezoelectricity up to 300 °C, which actualizes their applicability as piezoelectric devices with high thermal stability.

Lead-Free Piezoelectric Acceleration Sensor Built Using a (K,Na)NbO3 Bulk Ceramic Modified by Bi-Based Perovskites.

Piezoelectric accelerometers using a lead-free (K,Na)NbO3 (KNN) piezoceramic modified by a mixture of two Bi-based perovskites, Bi(Na,K,Li)ZrO3 (BNKLZ) and BiScO3 (BS), were designed, fabricated and characterized. Ring-shaped ceramics were prepared using a conventional solid-state reaction method for integration into a compression-mode accelerometer. A beneficial rhombohedral-tetragonal (R-T) phase boundary structure, especially enriched with T phase, was produced by modifying intrinsic phase transition temperatures, yielding a large piezoelectric charge coefficient d33 (310 pC/N) and a high Curie temperature Tc (331 °C). Using finite element analyses with metamodeling techniques, four optimum accelerometer designs were obtained with high magnitudes of charge sensitivity Sq and resonant frequency fr, as evidenced by two key performance indicators having a trade-off relation. Finally, accelerometer sensor prototypes based on the proposed designs were fabricated using the KNN-BNKLZ-BS ceramic rings, which exhibited high levels of Sq (55.1 to 223.8 pC/g) and mounted fr (14.1 to 28.4 kHz). Perfect charge-to-acceleration linearity as well as broad flat frequency ranges were achieved with excellent reliability. These outstanding sensing performances confirm the potential application of the modified-KNN ceramic in piezoelectric sensors.

A Theoretical and Empirical Investigation of Design Characteristics in a Pb(Zr,Ti)O3-Based Piezoelectric Accelerometer.

A theoretical and experimental study on the design-to-performance characteristics of a compression-mode Pb(Zr,Ti)O3-based piezoelectric accelerometer is presented. Using the metamodeling to approximate the relationship between the design variables and the performances, the constituent components were optimized so that the generated electric voltage, representing sensitivity, could be maximized at different set values of the resonant frequency (25-40 kHz). Four kinds of optimized designs were created and fabricated into the accelerometer modules for empirical validation. The accelerometer modules fabricated according to the optimized designs were highly reliable with a broad range of resonant frequency as well as sufficiently high values of charge sensitivity. The fixed (or mounted) resonant frequency was between 16.1-30.1 kHz based on the impedance measurement. The charge sensitivity decreased from 296.8 to 79.4 pC/g with an increase of the resonant frequency, showing an inverse relation with respect to the resonant frequency. The design-dependent behaviors of the sensitivity and resonant frequency were almost identical in both numerical analysis and experimental investigation. This work shows that the piezoelectric accelerometer can be selectively prepared with best outcomes according to the requirements for the sensitivity and resonant frequency, fundamentally associated with trade-off relation.

Piezoelectric Energy Harvesting from Two-Dimensional Boron Nitride Nanoflakes.

Two-dimensional (2D) piezoelectric hexagonal boron nitride nanoflakes (h-BN NFs) were synthesized by a mechanochemical exfoliation process and transferred onto an electrode line-patterned plastic substrate to characterize the energy harvesting ability of individual NFs by external stress. A single BN NF produced alternate piezoelectric output sources of ∼50 mV and ∼30 pA when deformed by mechanical bendings. The piezoelectric voltage coefficient (g11) of a single BN NF was experimentally determined to be 2.35 × 10-3 V·m·N-1. The piezoelectric composite composed of BN NFs and an elastomer was spin-coated onto a bulk Si substrate and then transferred onto the electrode-coated plastic substrates to fabricate a BN NFs-based flexible piezoelectric energy harvester (f-PEH) which converted a piezoelectric voltage of ∼9 V, a current of ∼200 nA, and an effective output power of ∼0.3 µW. This result provides a new strategy for precisely characterizing the energy generation ability of piezoelectric nanostructures and for demonstrating f-PEH based on 2D piezomaterials.

Design Optimization of Bulk Piezoelectric Acceleration Sensor for Enhanced Performance.

While seeking to achieve high performances of a bulk piezoelectric acceleration sensor, we investigated the behavior of the design variables of the sensor components and optimized the sensor design using a numerical simulation based on piezoelectric analysis and metamodeling. The optimized results demonstrated that there was an exponential dependency in the trade-off relation between two performance indicators, the electric voltage and the resonant frequency, as induced by the design characteristics of the sensor. Among the design variables, a decrease in the base height and epoxy thickness and an increase in the piezo element's inner diameter had a positive effect on two performances, while the head dimensions (diameter and height) exhibited the opposite effect on them. The optimal sensor designs are proposed within the valid range of resonant frequency (25-47.5 kHz). Our redesign of a commercial reference sensor improved the resonant frequency by 13.2% and the electric voltage by 46.1%.

Proposal of a rhombohedral-tetragonal phase composition for maximizing piezoelectricity of (K,Na)NbO3 ceramics.

Great progress in the field of piezoelectricity of (K,Na)NbO3 (KNN) lead-free ceramics, driven by emerging rhombohedral-tetragonal (R-T) phase boundary, has instigated research activity regarding elaborate controls of the phase boundary structure. Through phase-microstructure-property mapping in KNN ceramics doped with Bi-containing perovskite oxides, in this study we for the first time report the existence of a certain R-T phase boundary state by which to create maximum piezoelectric response in KNN systems. This phase boundary condition is usually comprised of approximately 15% R phase and 85% T phase, regardless of the choice of dopant material. Any deviation from this phase composition, either by inclusion of orthorhombic (O) phase or by enrichment of R phase, has a negative effect on the value of d33. These findings can provide useful guidance for chemical doping control associated with the type of phase boundary and the phase composition for advanced KNN-based materials.

Aging-resistant nanofluids containing covalent functionalized boron nitride nanosheets.

Developing a thermally stable nanofluid that can maintain good thermo-conductive and flow performance at moderate or elevated temperatures for prolonged periods of time is a great challenge in heat transfer applications. Here, the thermal conductivity and rheological properties as well as their thermal stability characteristics of a nanofluid containing two-dimensional (2D) hexagonal boron nitride nanosheets (h-BNNSs) in ethylene glycol (EG) are presented, in comparison with those for a graphene oxide (GO) nanofluid as a counterpart. In place of a surfactant, hydroxyl functional groups covalently bound to the BNNS surface provided excellent compatibility and stable dispersion of the particles within EG at temperatures up to 90 °C. Owing to the percolation effect of the 2D sheets, the thermal conductivity of the EG base fluid was significantly enhanced by 80% at 5 vol% of BNNS, superior to that of the GO fluid. Moreover, the BNNS fluids exhibited excellent long-term stability at 90 °C for 5 d without loss of their high thermal conductivity, low viscosity and electrical insulating property, whereas the GO fluids underwent thermal degradation with irreversible particle aggregation and increasing viscosity due to the selective chemical reduction of the surface functional groups (i.e., C-O groups) of the GO.

Rapid and direct synthesis of complex perovskite oxides through a highly energetic planetary milling.

The search for a new and facile synthetic route that is simple, economical and environmentally safe is one of the most challenging issues related to the synthesis of functional complex oxides. Herein, we report the expeditious synthesis of single-phase perovskite oxides by a high-rate mechanochemical reaction, which is generally difficult through conventional milling methods. With the help of a highly energetic planetary ball mill, lead-free piezoelectric perovskite oxides of (Bi, Na)TiO3, (K, Na)NbO3 and their modified complex compositions were directly synthesized with low contamination. The reaction time necessary to fully convert the micron-sized reactant powder mixture into a single-phase perovskite structure was markedly short at only 30-40 min regardless of the chemical composition. The cumulative kinetic energy required to overtake the activation period necessary for predominant formation of perovskite products was ca. 387 kJ/g for (Bi, Na)TiO3 and ca. 580 kJ/g for (K, Na)NbO3. The mechanochemically derived powders, when sintered, showed piezoelectric performance capabilities comparable to those of powders obtained by conventional solid-state reaction processes. The observed mechanochemical synthetic route may lead to the realization of a rapid, one-step preparation method by which to create other promising functional oxides without time-consuming homogenization and high-temperature calcination powder procedures.

Targeted Tumor Therapy Based on Nanodiamonds Decorated with Doxorubicin and Folic Acid.

The fabrication of nanodiamond (ND)-based drug carriers for tumor-targeted drug delivery is described. The ND clusters with an average size of 52.84 nm are fabricated using a simple fluidic device combined with a precipitation method and then conjugated with folic acid (FA) and doxorubicin (Dox) via carbodiimide chemistry to obtain FA/Dox-modified ND (FA/Dox-ND) clusters. Cell culture experiments revealed that KB (folate receptor-positive) cells are preferentially ablated by FA/Dox-ND clusters compared to A549 (folate receptor-negative) cells. In vivo results revealed that FA/Dox-ND clusters are specifically accumulated in tumor tissues after intravenous injection into tumor-bearing mice, effectively reducing the volume of tumor. Based on these results, this study suggests that FA/Dox-ND clusters can be a good candidate as tumor-targeted nanovehicles for delivery of antitumor drug.

Decreased Total Antioxidant Activity in Major Depressive Disorder Patients Non-Responsive to Antidepressant Treatment.

OBJECTIVE: This study aimed to evaluate the total antioxidant activity (TAA) in patients with major depressive disorder (MDD) and the effect of antidepressants on TAA using a novel potentiometric method. METHODS: Twenty-eight patients with MDD and thirty-one healthy controls were enrolled in this study. The control group comprised 31 healthy individuals matched for gender, drinking and smoking status. We assessed symptoms of depression using the Hamilton Depression Rating Scale (HAMD) and the Beck Depression Inventory (BDI). We measured TAA using potentiometry. All measurements were made at baseline and four and eight weeks later. RESULTS: There was a significant negative correlation between BDI scores and TAA. TAA was significantly lower in the MDD group than in controls. When the MDD group was subdivided into those who showed clinical response to antidepressant therapy (response group) and those who did not (non-response group), only the non-response group showed lower TAA, while the response group showed no significant difference to controls at baseline. After eight weeks of antidepressant treatment, TAA in both the response and non-response groups was similar, and there was no significant difference among the three groups. CONCLUSION: These results suggest that the response to antidepressant treatment in MDD patients might be predicted by measuring TAA.

Precisely Determining Ultralow level UO2(2+) in Natural Water with Plasmonic Nanowire Interstice Sensor.

Uranium is an essential raw material in nuclear energy generation; however, its use raises concerns about the possibility of severe damage to human health and the natural environment. In this work, we report an ultrasensitive uranyl ion (UO2(2+)) detection method in natural water that uses a plasmonic nanowire interstice (PNI) sensor combined with a DNAzyme-cleaved reaction. UO2(2+) induces the cleavage of DNAzymes into enzyme strands and released strands, which include Raman-active molecules. A PNI sensor can capture the released strands, providing strong surface-enhanced Raman scattering signal. The combination of a PNI sensor and a DNAzyme-cleaved reaction significantly improves the UO2(2+) detection performance, resulting in a detection limit of 1 pM and high selectivity. More importantly, the PNI sensor operates perfectly, even in UO2(2+)-contaminated natural water samples. This suggests the potential usefulness of a PNI sensor in practical UO2(2+)-sensing applications. We anticipate that diverse toxic metal ions can be detected by applying various ion-specific DNA-based ligands to PNI sensors.

Cellular Uptake Behavior of Doxorubicin-Conjugated Nanodiamond Clusters for Efficient Cancer Therapy.

This paper describes the design and fabrication of doxorubicin (Dox)-conjugated nanodiamond (ND) clusters with controlled sizes and cellular uptake behaviors of free Dox and Dox-conjugated ND clusters. The ND clusters with an average size of 45.84 nm exhibited a higher amount of cellular uptake as compared to the ND clusters with larger sizes. The amount of Dox taken up as free Dox increased initially and then decreased over time. In contrast, the amount of Dox taken up as Dox-ND clusters continuously increased and reached a plateau, resulting in high ablation efficiency. At the same Dox concentration, the cell viabilities after treatment with free Dox and Dox-ND clusters were 26.38 and 5.31%, respectively. The Dox-ND clusters potentially could be employed as efficient drug carriers for efficient cancer therapy.

Anti-oxidant and natural killer cell activity of Korean red ginseng (Panax ginseng) and urushiol (Rhus vernicifera Stokes) on non-alcoholic fatty liver disease of rat.

Anti-oxidative and immunologic effects of the Korea red ginseng (KRG; Panax ginseng) and urushiol (Rhus vernicifera Stokes) on non-alcoholic fatty liver disease (NAFLD) were evaluated. Forty-five rats (five Long-Evans Tokushima Otsuka and 40 Otsuka Long-Evans Tokushima Fatty [OLETF] rats) received chew diets for 10months; after this period. The OLETF rats were divided into the following four groups according to diet for 2months: NAFLD (chew), KRG (chew+KRG [200mg/kg/day]), urushiol (chew+urushiol [0.5mg/kg/day]), and ursodeoxycholic acid (UDCA) (chew+UDCA [15mg/kg/day]) groups. Liver function, lipid profiles and anti-oxidant activity of liver and serum, natural killer (NK) cell activity, and pathology were compared. In KRG and urushiol groups, the level of serum triglyceride ([302.0±70.4 and 275.2±63.8] vs. 527.7±153.3mg/dL) were lower compared with that of NAFLD group (p<0.05). The levels of HDL-cholesterol (liver tissue: [4.8±0.2 and 4.8±0.5] vs. 4.2±0.2mg/g) and NK cell activity ([3485±910 and 3559±910] vs. 2486±619 counts) were significantly higher than those of the NAFLD group (p<0.001). Inflammation with neutrophil infiltration was observed in only two rats in the NAFLD group. These results suggest that 2months of oral KRG or urushiol administration improves lipid profiles and stimulates NK cell activity, while inhibiting steatohepatitis in OLEFT rats.

Reliability evaluation of nano-bi/silver paste sensor electrode for detecting trace metals.

The reliability of sensor characteristics for a nano-bismuth (Bi)/silver (Ag) paste electrode has been investigated by comparison with Hg/Bi film electrodes in terms of accuracy and precision. Using Ag paste instead of carbon paste as a conducting layer, the sensitivity and detection limit of the sensor electrode were more enhanced due to a lower electrical conductivity of Ag. For the evaluation of detecting ability, the Zn, Cd, and Pb ion concentrations of the prepared standard solutions were experimentally measured on Hg film, Bi film, and nano-Bi electrodes using anodic stripping voltammetry. A nano-Bi electrode can detect Zn, Cd, and Pb ions at 0.1 ppb with higher precision and accuracy compared with Hg film and Bi film electrodes. From the trace analyses of Zn, Cd, and Pb ions in commercial drinking water and river water using a nano-Bi electrode and inductively coupled plasma (ICP) technique, it was concluded that the nano-Bi electrode exhibited excellent sensing characteristics with high reliability, and could detect even traces of Zn, Cd, and Pb ions that were not detected by the ICP method.

Surface modification to improve hydrophobicity of detonation nanodiamond.

In this work, surface treatment of nanodiamonds (NDs) produced by a detonation technique has been conducted using oleic acid and dodecylamine in order to achieve a stable dispersion in oil. From Fourier transform infrared spectroscopy (FTIR) analyses, it was found that the NDs have various surface functional groups such as -NH2, -COOH, -OH, etc. By inducing covalent bonding between the carboxyl group of oleic acid and the amine group of the ND surface with high chemical reactivity, NDs were well-dispersed in oil for a lengthy period of time. High resolution transmission electron microscopy (HRTEM) images indicate that the surface treatment with oleic acid is highly effective in breaking down the aggregates of NDs into smaller sized particles. The dispersion stabilities of the oils containing as-received NDs and surface treated NDs were compared to each other using Turbiscan measurement.

Round-robin test on thermal conductivity measurement of ZnO nanofluids and comparison of experimental results with theoretical bounds.

Ethylene glycol (EG)-based zinc oxide (ZnO) nanofluids containing no surfactant have been manufactured by one-step pulsed wire evaporation (PWE) method. Round-robin tests on thermal conductivity measurements of three samples of EG-based ZnO nanofluids have been conducted by five participating labs, four using accurate measurement apparatuses developed in house and one using a commercial device. The results have been compared with several theoretical bounds on the effective thermal conductivity of heterogeneous systems. This study convincingly demonstrates that the large enhancements in the thermal conductivities of EG-based ZnO nanofluids tested are beyond the lower and upper bounds calculated using the models of the Maxwell and Nan et al. with and without the interfacial thermal resistance.

Effect of phase stability degradation of bismuth on sensor characteristics of nano-bismuth fixed electrode.

Effect of phase stability degradation of bismuth on sensor characteristics of nano-bismuth fixed electrode has been investigated using square-wave anodic stripping voltammetry technique, scanning electron microscopy (SEM) and X-ray diffraction (XRD) spectroscopy. From the analyses of square-wave anodic stripping voltammograms (SWASV) repetitively measured on the nano-bismuth fixed electrode, it was found that the oxidation peak currents dropped by 81%, 68% and 59% for zinc, cadmium and lead, respectively, after the 100th measurement (about 400 min of operation time). The sphere bismuth nanoparticles gradually changed to the agglomerates with petal shape as the operation time increased. From the analyses of SEM images and XRD patterns, it is confirmed that the oxidation of Bi into BiOCl/Bi(2)O(2)CO(3) and the agglomeration of bismuth nanoparticles caused by the phase change decrease a reproducibility of the stripping voltammetric response. Moreover, most of the bismuth becomes BiOCl at pH 3.0 and bismuth hydroxide, Bi(OH)(3) at pH 7.0, which results in a significant decrease in sensitivity of the nano-bismuth fixed electrode.

Hierarchical assembly of diphenylalanine into dendritic nanoarchitectures.

Highly ordered, multi-dimensional dendritic nanoarchitectures were created via self-assembly of diphenylalanine from an acidic buffer solution. The self-similarity of dendritic structures was characterized by examining their fractal dimensions with the box-counting method. The fractal dimension was determined to be 1.7, which demonstrates the fractal dimension of structures generated by diffusion limited aggregation on a two-dimensional substrate surface. By confining the dendritic assembly of diphenylalanine within PDMS microchannels, the self-similar dendritic growth could be hierarchically directed to create linearly assembled nanoarchitectures. Our approach offers a novel pathway for creating and directing hierarchical nanoarchitecture from biomolecular assembly.

Synthesis of nanocrystalline bismuth and its application to the detection of trace metals.

Surface modified carbon strip electrode with Bi nanopowder was suggested for a simultaneous analysis of Zn, Cd, and Pb ions by a square wave anodic stripping voltammetry, and the influence of the modifying Bi mass and particle size on the trace metal response was investigated. The Bi nanopowders with various particle size distributions were synthesized by an optimization of the gas condensation condition, in which a refractory crucible was applied for the evaporation of volatile Bi, and then immobilized on the surface of a working electrode. The result of the stripping measurements shows that when the modifying mass and the particle size of the Bi powder were in the range of 2 to 5 microg/cm2 and less than 300 nm, respectively, a well-developed and reproducible stripping response was obtained. The proposed "mercury-free" carbon strip electrode, modified with Bi nanopowder, is conveniently usable and directly applicable to a trace metal analysis without a pre-deposition of Bi and complicated surface polishing steps.

A study on electrophoretic deposition of Ni nanoparticles on pitted Ni alloy 600 with surface fractality.

In the present work, the electrophoretic deposition of Ni nanoparticles used for self-repairing of pits in organic suspension was investigated on pitted fractal Ni alloy 600 with respect to surface fractality of the pits. For this purpose, Ni nanoparticles prepared by levitation-gas condensation were dispersed into an ethanol solution with the addition of a dispersant. Four kinds of pitted fractal specimens with different surface fractal dimensions dF,surf were prepared by applying various anodic potentials above pitting potential to alloy 600 in aqueous 0.1 M NaCl solution. From the scanning electron microscopy (SEM) images, it was observed that the pits repaired under applied electric field E of 100 V cm-1 comprised more agglomerates of Ni nanoparticles than those repaired under E of 20 V cm-1. This suggests that the higher the value of E is, the more agglomerates of Ni nanoparticles are deposited on the specimen due to more depletion of OH- in suspension near the specimen surface. Moreover, the specimen with higher dF,surf gave a higher value of electrophoretic current Ip than one with lower dF,surf due to the increased electrochemical active area Aea of the specimen. From the above, it is concluded that the surface irregularities of the pit enhance the deposition of Ni nanoparticles on pitted fractal specimen during electrophoretic deposition.