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We fabricated Bi0.5(Na1-xKx)0.5TiO3 (BNKT) [x = 0.16–0.24] relaxor ferroelectric ceramics that undergo a transition from the non-ergodic state (NR) to the ergodic state (ER) using a conventional solid-state reaction method. Structural analysis was conducted using X-ray diffraction (XRD), and the electrical properties related to the polarization (P) and strain (S) resulting from the external electric field were analyzed. With an increase in the component ratio x, from 0.16 to 0.24, the remnant polarization (Pr) reduced continuously from ∼18 to ∼3 μC/cm2, respectively. Concomitantly, the form of the S-E loops changed from a butterfly-like shape to a sprout shape (in which the negative strain value (Sneg) that approaches 0 appears as a special feature), suggesting that the NR of the BNKT relaxor ferroelectric ceramic at x = 0.16 transitions to the ER as the composition ratio x increases. In particular, for x = 0.20, the inverse piezoelectric coefficient (d33*) achieved a maximum value of 386 p.m./V, while the value of the Pr was relatively low at ∼ 6 μC/cm2. To investigate the possible application as a wearable energy harvester, BNKT ceramic powders of various compositions were mixed with polydimethylsiloxane (PDMS) to fabricate flexible generator devices. The change in the output voltage and current as a function of the composition ratio x had a similar tendency as the change in the value of d33*, suggesting that the ER of relaxor ferroelectric ceramics with a large strain value is suitable for application in wearable energy harvesters.

Research Center for Dielectric Study was supported by the Korean Research Foundation from the government. In 1991, Professor Jang, Min-Soo along with 22 other professors, received a research grant of 7 billion won for 10 years, which enabled the Korean Ferroelectric Research Society to be competitive globally. The 9th International Meeting on Ferroelectricity, which is held every four years, was held in Seoul in 1997. The first dielectric joint symposium organized by condensed-matter physics and materials science researchers was held in 2005. The Korean Dielectrics Society was established at Muju resort in 2017, with Professors Tae Won Noh and Jaichan Lee representing the condensed-matter physics and materials science communities, respectively. Currently, more than 300 members are actively participating in the Korean Dielectric Society. To celebrate the 100th anniversary of ferroelectricity, which was fist discovered in Rochelle salt by Joseph Valasek in 1921, we organized a special session in the 2020 Korean Physics Society Fall Meeting.

A novel and facile hydrothermal route was designed to produce h-BN-C quantum dots (h-BN-C QDTs) using h-BN powder as a precursor and Potassium Sodium Tartare as an intercalant. The resulting yellow solution possessed mono or few-layers of quantum dots with an average size of ~2.5 nm. Due to the incorporation of functional groups (carbon, oxygen) on the surface of h-BN, an enhancement of photo luminescent magnitude and a blue shift were observed in photoluminescence spectra from h-BN-C QDTs solution. Further, h-BN-C QDTs exhibits a bright blue fluorescence under the irradiation by a 365 nm UV light. Next, h-BN QDTs was utilized as the dielectric active layer by using simple drop casting method between the electrodes and fabricated the nonvolatile resistive switching devices. The fabricated devices exhibited the nonvolatile bipolar resistive switching characteristics with 103 ON/OFF ratio and turned ON and OFF threshold voltages of −1.9 V and +1.4 V, respectively. Further, the switching mechanisms of h-BN-C QDTs were found to be space charged trapping. It provides a route toward tailoring the optical and electrical properties of the h-BN materials and can be utilized in the future potential applications.

In this study, we have proposed a simple method to produce temperature-dependent variablesize of MoS2 nanodots (NDTs) by using MoS2 powder as a pre-cursor and KNa-tartrate as the intercalant. Due to defects in MoS2, the optical properties are strongly modified and show blue luminescence under UV irradiation of MoS2 NDTs. The temperature variable is used to gradually introduce defects in 2D materials to obtain nanodots with different particle sizes. When the synthesis temperature is increased from 120 °C to 200 °C, the particle size is reduced from ~ 120 nm to ~ 2.5 nm. Next, an enhancement of photoluminescent magnitude and a red shift were observed in photoluminescence spectra from MoS2 NDTs solutions. These results offer a route toward tailoring the optical properties of 2D nanomaterials by controlling the size/temperature/synthesis method.

Ferroelectric and piezoelectric polymers have attracted great attention from many research and engineering fields due to its mechanical robustness and flexibility as well as cost-effectiveness and easy processibility. Nevertheless, the electrical performance of piezoelectric polymers is very hard to reach that of piezoelectric ceramics basically and physically, even in the case of the representative ferroelectric polymer, poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)). Very recently, the concept for the morphotropic phase boundary (MPB), which has been exclusive in the field of high-performance piezoelectric ceramics, has been surprisingly confirmed in P(VDF-TrFE) piezoelectric copolymers by the groups. This study demonstrates the exceptional behaviors reminiscent of MPB and relaxor ferroelectrics in the feature of widely utilized electrospun P(VDF-TrFE) nanofibers. Consequently, an energy harvesting device that exceeds the performance limitation of the existing P(VDF-TrFE) materials is developed. Even the unpoled MPB-based P(VDF-TrFE) nanofibers show higher output than the electrically poled normal P(VDF-TrFE) nanofibers. This study is the first step toward the manufacture of a new generation of piezoelectric polymers with practical applications.

We couple the spark plasma sintering (SPS) technique with the ball mill process to fabricate a new electro-chemo-mechanical functional carbon-metal oxide hybrid material. Graphene oxide (GO) or carbon nanotubes (CNT) carbon allotropes are mechanically mixed with gadolinium-doped ceria (CGO). SPS allows consolidating dense carbon-metal oxide hybrids with uniform morphology and high crystallinity. The carbon allotropes and SPS lead to highly reduced CGO. The metal oxide presents a chemically tuned grain boundary with highly oxygen defect concentration at the near-grain boundary region. The hybrid interface can hinder chemical oxidation at high-temperature depending on the carbon allotropy. As a result, the hybrid materials with CNT display high ionic conductivity and activation energy, reducing the space charge layer and charge distribution. This feature enhances the electromechanical properties at room temperature. We especially disclose electrostriction in the CNT-based hybrids superior to the pure CGO and follow a non- Newnham relation. Notably, integrating carbon materials with metal oxides using the SPS can generally be applied to synthesising a range of functional metal oxide composite.

Although there is considerable interest in BiFeO3 owing to its versatile physical properties, which make it suitable for a wide range of applications, its high leakage current is a significant limi...

We investigated the visible emission property of SrTiO3 (STO) single crystals irradiated with gammy-ray (γ-ray) at various total doses up to 900 kGy. The electric and optical absorption properties of the irradiated STO samples were hardly changed with the γ-ray irradiation, compared with those of un-irradiated STO. In contrast, the visible emission near 550 nm increased with the γ-ray dose increasing. While the development of the visible emission was indicative of the increase of oxygen vacancies inside STO by the γ-ray irradiation, the newly generated oxygen vacancies were not significantly harmful to the electric and optical properties of STO. We concluded that the STO single crystal should have a good tolerance against the damage by the γ-ray irradiation.

Recently the deleterious environmental impact of the lead used in many ferroelectric and piezoelectric devices has stimulated research into lead-free alternatives with comparable properties. Bismut...

We investigated the effects of gamma-ray (γ) irradiation on the morphology properties of (K0.5Na0.5)(Mn0.005Nb0.995)O3 (KNMN) thin films. The KNMN thin films were prepared on Pt/Ti/SiO2/Si substrate using a chemical solution deposition method through a spin-coating process and were subject to γ radiation at various total doses from 0–3000 kGy. The grain size of the KNMN films changed visibly with an increase in the total γ irradiation dose. Williamson-Hall plot analysis revealed that the microstrain of the films increased from 0.222% (at 0 kGy) to 0.266% (at 3000 kGy) after the irradiation. The observed variation of the morphology properties on the total dose might be mainly associated with the microstrain in Mn-doped KNN thin films. In addition the migration of defects and/or impurities bound inside the grain by the gamma-ray energy in Mn-doped KNN thin films can enhance the grain size decrease process. The mobile impurities in our polycrystalline samples can congregate at the domain boundary, wh...

We investigated the effect of the gamma-ray irradiation on the emission property of the Eu ion doped YVO 4 . We clearly observed that on exposure to the gamma-ray, sharp emission peaks originating from the Eu 3+ ions were suppressed dramatically. Instead, a broad emission feature near 470 nm, which was attributed to the Eu 2+ ions, emerged. The quantitative analysis on the emission spectra suggest that the valence state of the Eu ions in our samples was changed from 3 + to 2 + by the gamma-ray irradiation. The conversion of the valence state of the Eu ions was closely related to the formation of the oxygen vacancies induced by the gamma-ray irradiation.

In this study, a nanocomposite was successfully fabricated by mixing Pb(Zr,Ti)O3 (PZT) prepared by using the sol-gel method and functionalized multi-walled carbon nanotubes (MWCNTs). During this process, the effect of the change in the molar concentration of PZT on the crystallinity and the piezoelectric properties of the PZT in the nanocomposite was investigated. As the number of PZT coatings was increased from one to three, PZT was confirmed as having completely covered the MWCNT nanocomposite. Also, the tetragonality of PZT in the crystal structure was confirmed to have increased with increasing number of PZT coatings. Such an increase in crystallinity was followed by an increase in the ferroelectricity of the nanocomposite. A nano-generator was fabricated by using the nanocomposite fabricated as described above, and the characteristics of the nanogenerator were confirmed to have been improved with increasing number of coatings.

In this study, Pb(Zr,Ti)O3 (PZT) nanoparticles directly were successfully grown on carbon nanotubes by mixing a PZT solution prepared by using the sol-gel method with functionalized carbon nanotubes. During this process, the effects of the concentration of the PZT solution on the size, crystallinity, and composition ratio of the PZT nanoparticles on the carbon nanotubes were investigated. As the molar concentration of the PZT solution was increased from 0.05 M to 0.2 M, the particle size increased from 6.628 nm to 10.877 nm. As the size of the nanoparticles increased, the surface directions became more diverse. In terms of the crystal structure, the tetragonality of PZT increased with increasing molarity of the PZT solution. This improvement in crystallinity can be further linked to an increase in the ferroelectricity of the PZT-carbon nanotubes, so the nanocomposite fabrication method using carbon nanotubes is expected to affect the characteristics of ferroelectric materials and can be used to further improve the properties of those.

In this study, we prepared the bismuth layer-structured ferroelectric (BLSF)-type Bi 4 Ti 3 O 12 (BiT), Bi 3.25 La 0.75 Ti 3 O 12 (BLaT), and Bi 3.1 Nd 0.9 Ti 3 O 12 (BNdT) ceramics using the solid-state reaction method. The prepared ceramics were irradiated at room temperature by using a 60 Co gamma-ray source in a dose range of 0–3000 kGy with a dose rate of 10 kGy/h to compare the structure and electrical properties of the irradiated ceramics. The X-ray diffraction analysis shows that the BLSF structure was well formed in all ceramics without a secondary phase. There was no structural change such as grain size change and secondary phase formation despite the cumulative gamma-ray dose of 3000 kGy. A comparison of the electrical properties with gamma-ray irradiation shows that the BiT ceramics exhibits a larger reduction ratio compared to the BLaT and BNdT ceramics. The rate of change of the remnant polarization (2 P r ) value with the gamma-ray irradiation doses was − 14.2%, − 8%, and − 3.4% in BiT, BLaT, and BNdT ceramics, respectively, at a cumulative gamma-ray dose of up to 3000 kGy. Furthermore, the dielectric relaxation phenomenon in BiT ceramics at low frequency was observed when gamma rays of 1000 kGy or more were irradiated. Based on these results, in this study, we investigated the structure and electrical properties of BLSF ceramics with gamma-ray irradiation.

In this study, the surface-chemistry-dependent hydrophobicity and antibacterial properties of ITO films were examined. After annealing of the films, their surface root-mean-square roughness increased and remained the same regardless of the annealing environment. However, depending on the annealing environment (O 2 , N 2 , Ar, or vacuum), the contact angle increased with increasing Sn 2+ contents in the films. Furthermore, the antibacterial effect of the annealed films decreased regardless of the annealing environment. The depth-dependent chemical state determined by X-ray photoelectron spectroscopy showed an increase in the Sn content at the surfaces of all films. In particular, the as-grown film exhibited the highest Sn content at the surface and also the strongest antibacterial effect.

We investigated the emission properties of Bi 3.25 La 0.75 Ti 3 O 12 polycrystals and (K 0.5 Na 0.5 )(Mn 0.005 Nb 0.995 )O 3 thin films with strong gamma (γ)-ray irradiation by using temperature dependent photoluminescence spectroscopy. At the lowest temperatures, sizable visible emissions were identified for the γ-ray irradiated samples as well as un-irradiated ones. In both kinds of compounds, the visible emission intensity tended to be increased without changing the spectral shape, as the γ-ray dose increased. This indicates that the γ-ray irradiation should increase all kinds of already-existing defects evenly, without preferring the formation of some particular type of defect.

In photoelectrochemical (PEC) water splitting, charge separation and collection by the electric field in the photoactive material are the most important factors for improved conversion efficiency. Hence, ferroelectric oxides, in which electrons are the majority carriers, are considered promising photoanode materials because their high built-in potential, provided by their spontaneous polarization, can significantly enhance the separation and drift of photogenerated carriers. In this regard, the PEC properties of BiFeO3 thin-film photoanodes with different crystallographic orientations and consequent ferroelectric domain structures are investigated. As the crystallographic orientation changes from (001)pc via (110)pc to (111)pc, the ferroelastic domains in epitaxial BiFeO3 thin films become mono-variant and the spontaneous polarization levels increase to 110 μC/cm2. Consequently, the photocurrent density at 0 V vs. Ag/AgCl increases approximately 5.3-fold and the onset potential decreases by 0.180 V in the downward polarization state. It is further demonstrated that ferroelectric switching in the (111)pc BiFeO3 thin-film photoanode leads to an approximate change of 8,000% in the photocurrent density and a 0.330 V shift in the onset potential. This study strongly suggests that domain-engineered ferroelectric materials can be used as effective charge separation and collection layers for efficient solar water-splitting photoanodes.

Bismuth layer-structured ferroelectric (BLSF)-type Bi4Ti3O12 (BiT), Bi3.25La0.75Ti3O12 (BLaT), and Bi3.1Nd0.9Ti3O12 (BNdT) ceramics and intergrowth BLSF-type BiT-CaBi4Ti4O15 (CBTO), BLaT-CBTO, and BNdT-CBTO ceramics were prepared using the solid-state reaction method. The electrical and the high-temperature properties of the intergrowth BLSF ceramics were compared with those of BLSF ceramics to investigate the possibility of using the former for high-temperature applications. The X-ray diffraction (XRD) analysis revealed well-formed stable structures in all BLSF and intergrowth BLSF ceramics without any second-phase formation. When their electrical properties were examined, the intergrowth BLSF ceramics BiT-CBTO, BLaT-CBTO, and BNdT-CBTO were found to outperform the BLSF ceramics BiT, BLaT, and BNdT, respectively, in terms of the remanent polarization and piezoelectric coefficient values. Among the intergrowth BLSF ceramics, those doped with rare-earth ions La and Nd, i.e., BLaT-CBTO and BNdT-CBTO ceramics, were found to have improved electrical properties compared to the BiT-CBTO ceramics. In particular, the dielectric constants and the piezoelectric coefficients of the BNdT-CBTO ceramics were observed to be as high as 146 and 15.4 pC/N, respectively, which were 28% and 10% higher than those of BNdT ceramics. In the thermal depoling behavior measured to examine high-temperature stability, the intergrowth BLSF ceramics, compared to the BLSF ceramics, demonstrated improvements in the thermal depoling temperature ranging from 100 to 300 °C.

We investigated the changes in the emission characteristics of SrTiO3 (STO) single crystals under control of oxygen vacancies by using gamma-ray irradiation. The photoluminescence spectroscopy is useful in probing oxygen vacancies, since the intensity of the visible emission is nearly proportional to the amount of oxygen vacancies. The STO samples were prepared in the directions of (100), (110) and (111). The unirradiated samples were found to show visible emissions near 500 nm, indicating they should have initially had some oxygen vacancies. With the gamma-ray irradiation increasing up to 100 kGy, the visible emission was found to increase for all three directions of STO samples. Interestingly, the variation in emission was dependent on the surface orientation of the STO: the intensity variation was greatest in the (111) sample. We discussed our results in relation to the surface energy of the STO.

The phase boundary structure of (K,Na)NbO3 piezoelectric ceramic was modified by doping with Bi(Na,K,Li)ZrO3 and BiGaO3 through normal solid-state sintering. Rietveld refinements by X-ray diffraction revealed that the Bi(Na,K,Li)ZrO3/BiGaO3 co-doping in (K,Na)NbO3 led to a multi-phase structure at room-temperature, effectively moving the rhombohedral-orthorhombic (R-O) and orthorhombic-tetragonal (O-T) polymorphic phase transition temperatures close to the room temperature region. Increased levels of doping also generated a structural transition, i.e., triphasic R-O-T to diphasic R-T (T-rich) and finally to R-T (R-rich), contributing to shrinkage of the O phase as well as the increase of R phase fraction. A sensitive influence of the BiGaO3 doping (0.001 mole fraction level) on the structural properties such as the phase and microstructure was shown, resulting from the effect of the super-tetragonal structure of BiGaO3. The d33 property was strongly dependent on the phase and its volume fraction, in addition to the grain sizes. Eventually, enhanced and balanced properties of the piezoelectric coefficient and Curie temperature (d33 = 309 pC/N, TC = 343 &deg, C) were obtained when the doped ceramic had a T-rich (86%) R-T structure.

A new type of coaxial hetero‐structured MoS2/SnO2 nanotube (MS‐NT) array is rationally designed for flexible visible light photodetector. Herein, a suitable solution for fabricating MS‐NT comprising SnO2 with controlled thickness and strain is proposed. The thickness of SnO2 deposited on MoS2 nanotubes are delicately manipulated by adjusting atomic layer deposition (ALD) cycles, which cause the internal tensile strain of the hybrid nanotubes. The photocurrent of the MS‐NT‐based photodetector exhibits high photoresponsivity values of 198.4 mA W‐1 and external quantum efficiency of 0.78%. In the analysis, a linear correlation between the excitation power and the photocurrent extracted from the MNT‐based devices is discerned. At the same time, a superlinearity of photocurrent in the MS‐NT arrays‐based device is found. Density functional theory calculations are adopted to unveil the strong correlation between the strain, bandgap, and photocurrent of the MS‐NT, which is a decisive factor for understanding the experimental evidences. The detailed mechanism for enhance photoresponsivity is further suggested for the strain‐tailored MS‐NT arrays‐based device. Such peculiar properties are expected to open a new chapter in the era of smart optical devices that require low driving voltage and high power efficiency.

We investigated the emission properties of Eu ion-doped ABaPO4 (ABaPO4:Eu, A = Li, Na, and K) in which the valence state of the Eu ions was controlled by annealing in various ambients, gamma-ray (γ-ray) irradiation, and hydrogen ion (H+) implantation. We synthesized the ABaPO4:Eu samples by solid-state reaction in air. The as-synthesized samples showed sharp red emission near 600 nm, which originated from Eu3+ ions. Interestingly, annealing under H2 ambient changed the valence state of the Eu ions from 3+ to 2+, which was indicated by the disappearance of the red emission and concurrent emergence of strong blue emission. After subsequent annealing in O2 atmosphere, the red emission of Eu3+ was recovered. The reversible switching between the 2+ and 3+ states was found to be repeatable by alternating H2 and O2 annealing. The valence state was also changed from 3+ to 2+ by H+ implantation and γ-ray irradiation of the as-synthesized samples, possibly owing to the formation of oxygen vacancies. Our results suggest that the luminescence color of the ABaPO4:Eu phosphors can be controlled within a range from red to blue by simple annealing in various ambients.

The piezoelectric and ferroelectric properties of 0.76(Bi0.5Na0.5)TiO3–0.04(Bi0.5Li0.5)TiO3–0.2(Bi0.5K0.5)TiO3 (abbreviated as 0.76BNT–0.04BLT–0.2BKT) ceramics were investigated to clarify the optimal sintering temperature, and the vibration characteristics were examined for a compression-mode accelerometer assembly in which 0.76BNT–0.04BLT–0.2BKT ceramics sintered at the optimized temperature served as the piezoelectric elements. The increase in the grain size of the 0.76BNT–0.04BLT–0.2BKT ceramics with the sintering temperature provides a beneficial contribution to the piezoelectric coefficient; however, it detrimentally contributes to the depolarization temperature. The charge sensitivity of the prototype accelerometers was evaluated with changes in the seismic mass and the layer number of the piezoceramics. The deviation between the theoretical and measured values of charge sensitivity was less than 10%.

Pb-free ferroelectric Bi4Ti3O12-CaBi4Ti4O15 (BIT-CBT) ceramics were manufactured using a solid-state reaction method. Structural analysis by using X-ray diffraction confirmed the presence of a second phase of Bi2Ti2O7, and the surface depth X-ray diffraction analysis revealed that this phase existed only on the surface. This second phase appears to have been caused by the volatilization of Bi ions at high sintering temperatures. For resolution of the issue of volatilization of Bi ions and manufacture of BIT-CBT ceramics with a single phase, Bi2O3 powder was added to the BIT-CBT mixture, and a powder-bed method, in which pellets were covered with BIT-CBT powder, was used to manufacture the ceramic. The piezoelectric coefficient of the single-phase BIT-CBT ceramics was 12.4 pC/N while the residual polarization and the coercive electric field were 11.3 μC/cm2, and 125 kV/cm, respectively. The results suggest that single-phase BIT-CBT ceramics are suitable for the manufacture of elements incorporating these electrical characteristics.

We investigated the visible emission property of Pb(Zr,Ti)O3 (PZT) thin films irradiated with gammy-ray (γ-ray) irradiated at various total doses up to 1000 kGy. The PZT thin films were prepared on Pt/Ti/SiO2/Si substrates by using a sol-gel method with a spin-coating process. The visible emission was found to emerge near 550 nm upon γ-ray irradiation, and the intensity of the emission increased with increasing dose. The spectrum of the γ-ray-induced emission was quite narrow, which was quite different from that due to normal defects such as oxygen vacancies. We suggest that the γ-ray irradiation generates inside the PZT films a specific type of defect state that can be detected by using low-temperature photoluminescence spectroscopy.

Dielectric composites fabricated by combining multi-walled carbon nanotubes (MWCNT) and PbTiO 3 (PTO) powder were prepared using a sol–gel process. Well-dispersed PTO powder with various volume ratios of MWCNT was compressed to form a pellet, and then silver electrodes were coated on both sides for electrical measurements. The PTO–MWCNT composite with 0.4 vol% MWCNT showed the highest dielectric constant (912 at 1 kHz), which is approximately 25 times larger than that (37 at 1 kHz) of a pure PbTiO 3 pellet. Furthermore, a strong frequency dependence of the dielectric constant in the low frequency range was shown for the PTO–MWCNT composites. Interfacial effects related to dielectric relaxation in composite materials were used to explain an observed increase of the dielectric constant near the percolation threshold.

We investigated the effects of gamma-ray (γ) irradiation on the electrical properties of (K0.5Na0.5) (Mn0.005Nb0.995)O3 (KNMN) thin films. The KNMN thin films were prepared on Pt/Ti/SiO2/Si substrate using a chemical solution deposition method through a spin-coating process and were subject to γ radiation at various total doses from 0 to 3000 kGy. The structural properties as well as the ferroelectric and dielectric properties of the prepared films were examined before and after γ irradiation. We found that their crystalline quality did not vary significantly with an increase in the total dose. It was also observed that the remnant polarization value of the films decreased by ∼10%, but the films maintained ferroelectricity even after irradiation up to 3000 kGy. In addition, the dielectric constant of the films decreased with the total dose. The observed variation of the electrical properties on the total dose might be mainly associated with the mobile defects in Mn-doped KNN thin films such oxygen vacancy and the stored energy gained from gamma-rays.

We report the effects of the phase, i.e., the rhombohedral (R), orthorhombic (O) and tetragonal (T) phase, within a polymorphic phase boundary on the piezoelectric properties of (K,Na)NbO3 ceramics doped with Bi(Na,K,Li)ZrO3 and (Bi,Na)TiO3. For the R-O-T phase boundary, the formation of an R-T phase boundary by O phase shrinkage is clearly beneficial to enhance the piezoelectric performance, whereas the enrichment of the T phase in the R-T phase boundary negatively affects the piezoelectric activity. Electrical poling in relation to the piezoelectric property strongly depends on the nature of the phase boundary, requiring the optimization of temperatures corresponding to the R-T phase boundary without the O phase.

In this work, we investigated the effects of the pyrolysis temperature on the structural, Raman, and infrared properties of PbTiO3 nanotubes (PTO-NTs). The PTO-NTs were synthesized by spin coating a sol-gel solution on porous anodic alumina membranes, followed by the pyrolysis step at 400 − 600 ℃. Then, PTO-NTs were finally crystallized at 600 − 700 ℃ in an oxygen atmosphere to get the perovskite phase. The PTO-NTs had an outer diameter of about 420 nm and a wall thickness of about 10 nm. X-ray diffraction patterns showed that the tetragonality (c/a) increased from 1.019 to 1.028 as the pyrolysis temperature was increased from 400 to 600 ℃. Raman spectroscopy showed that the phonon modes of A 1(nTO) and E(nTO) increased with a redshift of the A 1(3TO) mode as the pyrolysis temperature was increased. In the Fourier-transform infrared spectra of PTO-NTs embedded in the porous anodic alumina membrane, the transmittance of the band at 499 cm−1 increased as the pyrolysis temperature was increased, which might be due to an increase in the tetragonality.

A novel three-dimensional transition metal dichalcogenide (TMD) structure consisting of seamless hollow nanoflakes on two-dimensional basal layers was synthesized by a one-step chemical vapor deposition method. Here, we demonstrate that the as-grown nanoflakes are formed on an organic promoter layer which served as a positive template and are swollen at the grain boundaries by the bubbling effect. TMD nanosheets with hollow nanoflakes are successfully applied as chemical sensors, and it was found that their gas adsorption property is strongly related to the internal strain gradient resulting from the variation in the lattice parameter. This result is consistent with the theoretical prediction in previous studies. Our chemical vapor deposition-based approach is an efficient way to generate TMD-based nanostructures over a large surface area for various practical applications such as chemical sensors.

A CaBi 4 Ti 4 O 15 (CBTO) ceramic in which the Bi 2 O 3 concentration was controlled from 0 to 10 wt% was fabricated using a solid-state reaction method. Structural analysis by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) indicated differences in the preferred grain orientation and size of the plate-like grains according to the Bi 2 O 3 concentration. The orientation of plate-like grains was also found to vary with the Bi 2 O 3 concentration. There was no noticeable change trend of dielectric properties with different Bi 2 O 3 concentrations. Relatively low dielectric constants (about 135) were exhibited by the CBTO ceramic with 1 wt% Bi 2 O 3 and CBTO ceramic with 10 wt% Bi 2 O 3 only, and similar values (about 150) were exhibited by the other ceramics. The dielectric loss exhibited a low value in the range of 0.01–0.09 for all samples (frequency range of 1–100 kHz). Regarding the ratio changes of the piezoelectric coefficient ( d 33 ) and the ratio of a -axis orientation of plate-like grains, the trends of these two values were shown to be similar. These results suggest that the addition of Bi 2 O 3 greatly influences the microstructure of CBTO ceramics, including the grain size and orientation of plate-like grains. In particular, the change in the preferred grain orientation is closely related to the change in the piezoelectric properties.

We investigated the temperature-dependent emission property of ferroelectric Pb(Zr,Ti)O 3 (PZT) nanotubes with variation of the outer diameter from 60 nm to 420 nm at a fixed wall-thickness (25 nm). The PZT nanotubes were synthesized in the sol–gel template directed method with a spin-coating process. While the emission peak positions show a red-shift at lower temperatures commonly for all the nanotubes, interestingly, the temperature dependence of the peak position depends strongly on the nanotube diameter. These results are discussed in terms of the template and geometrical shape effects on the emission property of the PZT nanotubes.

In this study, porous anodic alumina (PAA) was fabricated using oxalic acid and phosphoric acid as electrolytes, and the effects of impurities on the phase transition of PAA according to changes in the heat-treatment temperature were investigated. The average pore diameter of PAA fabricated using oxalic acid and phosphoric acid increased from 43 nm to 64 nm and from 145 nm to 183 nm, respectively, in proportion to the increase in the heat-treatment temperature. An X-ray diffraction (XRD) structure analysis revealed the structure of PAA fabricated in oxalic acid to be amorphous at or below 800°C and it changed to γ-alumina at 850°C. At higher temperatures, as the heattreatment temperature was increased, a coexistence of γ- and δ-alumina phases was observed in the 900–1000°C range, and the existence of δ-alumina was observed only at 1050°C. Finally, at 1100°C, a coexistence of δ- and α-alumina phases was observed. On the other hand, for PAA fabricated in phosphoric acid, while an amorphous structure appeared at or below 800°C, as was the case with PAA fabricated in oxalic acid, only δ-alumina existed in the 850–1100°C range. On the basis of 27Al magic-angle-spinning nuclear magnetic resonance (MAS NMR) and Fourier transform infrared spectrometry (FT-IR) results, we concluded that such a discrepancy in the phase transition was attributable to interactions between impurities originating from the electrolytes.

We investigated the strain effect on temperature-dependent photoluminescence property in the clamped (with template) and free-standing (without template) PbTiO 3 (PTO) nanotubes. The wall-thickness of nanotubes was varied from 25 to 80 nm with the outer diameter fixed to 420 nm. While all nanotubes show sizable green/yellow emission, the temperature dependent shift of the emission energy is significantly suppressed in the clamped PTO nanotubes, which is attributed to the lattice strain driven by the template clamping. This clamping effect is more significant for thinner nanotubes. Even in the free-standing PTO nanotubes the temperature-dependence of emission is affected by the wall-thickness. Our finding is the clear manifestation of the template and geometrical shape effect on the optical property of the nanotubes.

We report the influence of annealing temperature on Pb(Zr,Ti)O3 nanoparticles (PZT NPs) grown on multi-walled carbon nanotubes (MWCNTs). The nanocomposites consist of PZT NPs and MWCNTs that were successfully prepared by using a sol-gel process, followed by an injection using a syringe filter and then by rapid thermal annealing. Field-emission transmission electron microscopy (FETEM) indicated that as the annealing temperature was increased, the shape and the crystallinity of the PZT NPs on the MWCNTs changed from an amorphous structure to the perovskite phase of PZT. Raman spectroscopy showed that the ratio of the intensity of G band to that of the D band, which indicates the crystal purity of the MWCNTs, decreased from 0.57 to 0.55 when the annealing temperature was increased from 500 to 700 °C. A separate distribution of elemental C in the PZT NPs on the MWCNTs annealed at 600 °C was directly observed via energy dispersive X-ray spectroscopy.

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.

We report the phase evolution of Pb(Zr0.52Ti0.48)O3 nanotubes (PZT-NTs), from the pyrochlore to perovskite phase, with an outer diameter of about 420 nm and a wall thickness of about 10 nm. The PZT-NTs were fabricated in pores of porous anodic alumina membrane (PAM) using a spin coating of PZT sol-gel solution and subsequent annealing at 500-700 degrees C in oxygen gas. The pyrochlore phase was found to be formed at 500 degrees C, and also found not to be transformed into the perovskite phase, even though annealing was performed at higher temperatures to 700 degrees C. Elementary distribution analysis of PZT-NTs embedded in PAM reveal that Pb diffusion from nanotubes into pore walls of PAM is one of the main reasons. By employing firstly an additional PbO coating on the pyrochlore nanotubes and then subsequent annealing at 700 degrees C, we have successfully achieved an almost pure perovskite phase in nanotubes. These results suggest that PbO acts as a Pb-compensation agent in the Pb- deficient PZT-NTs. Moreover, our method can be used in the synthesis of all metal-oxide materials, including volatile elements.