Composite-based piezoelectric devices are extensively studied to develop sustainable power supply and selfpowered devices owing to their excellent mechanical durability and output performance. In this study, we design a leadfree piezoelectric nanocomposite utilizing (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 (BCTZ) nanomaterials for realizing highly flexible energy harvesters. To improve the output performance of the devices, we incorporate porous BCTZ nanowires (NWs) into the nanoparticle (NP)-based piezoelectric nanocomposite. BCTZ NPs and NWs are synthesized through the solidstate reaction and sol-gel-based electrospinning, respectively; subsequently, they are dispersed inside a polyimide matrix. The output performance of the energy harvesters is measured using an optimized measurement system during repetitive mechanical deformation by varying the composition of the NPs and NWs. A nanocomposite-based energy harvester with 4:1 weight ratio generates the maximum open-circuit voltage and short-circuit current of 0.83 V and 0.28 A, respectively. In this study, self-powered devices are constructed with enhanced output performance by using piezoelectric energy harvesting for application in flexible and wearable devices.

BNKT Ceramics, one of the representative Pb free based piezoelectric ceramics, constitutes a perovskite(ABO3) structure. At this time, the perovskite structure (ABO3) is in the form where the corners of the octahedrons are connected, and in the unit cell, two ions, A and B, are cations, A ion is located at the body center, B ion is located at each corner, and an anion O is located at the center of each side. Since Bi, Na, and K sources constituting the A site are highly volatile at a sintering temperature of 1100℃ or higher, it is difficult to maintain uniformity of the composition. In order to solve this problem, there should be suppression of volatilization of the A site material or additional compensation of the volatilized. In this study, the basic composition of BNKT Ceramics was set to Bi0.5(Na0.78K0.22)0.5TiO3 (= BNKT), and volatile site (Bi, Na, and K sources) were coated in the form of a shell to compensate additionally for the A site ions. In addition, the physical and electrical properties of BNKT and its coated with shell additives(= @BNK) were compared and analyzed, respectively. As a result of analyzing the crystal structure through XRD, both BNKT(Core) and @BNK(Shell) had perovskite phases, and the crystallinity was almost similar. Although the Curie temperature of the two sintered bodies was almost the same (TC = 290 ~ 300 ℃), it was confirmed that the d33 (piezoelectric coefficient) and Pr (residual polarization) values were different. The experimental results indicated that the additional compensation for a shell additive causes the coarsening, resulting in a decrease in sintering density and Pr(remanent polarization). However, coating shell additives to compensate for A site ion is an effective way to suppress volatilization. Based on these experimental results, it would be the biggest advantage to develop an eco-friendly material (Lead-free) that replaced lead (Pb), which is harmful to the human body. This lead-free piezoelectric material can be applied to a biomedical device or products(ex. earphones (hearing aids), heart rate monitors, ultrasonic vibrators, etc.) and skin beauty improvement products (mask packs for whitening and wrinkle improvement).

The volatilization of alkali ions in (K,Na)NbO3 (KNN) ceramics was inhibited by doping them with alkaline earth metal ions. In addition, the grain growth behavior changed significantly as the sintering duration (ts) increased. At 1,100 °C, the volatilization of alkali ions in KNN ceramics was more suppressed when doped with alkaline earth metal ions with smaller ionic size. A Ca2+-doped KNN specimen with the least alkali ion volatilization exhibited a microstructure in which grain growth was completely suppressed, even under long-term sintering for ts = 30 h. The grain growth in Sr2+-doped and Ba2+-doped KNN specimens was suppressed until ts = 10 h. However, at ts = 30 h, a heterogeneous microstructure with abnormal grains and small-sized matrix grains was observed. The size and number of abnormal grains and size distribution of matrix grains were considerably different between the Sr2+-doped and Ba2+-doped specimens. This microstructural diversity in KNN ceramics could be explained in terms of the crystal growth driving force required for two-dimensional nucleation, which was directly related to the number of vacancies in the material.

(Bi1/2Na1/2)TiO3 (BNT)-based ceramics are considered promising candidates for actuator application owing to their excellent electromechanical strain properties However, to obtain large strain properties, there remain several issues such as thermal stability and high operating fields. Therefore, this study investigates a reduction of operating field in (0.98-x)Bi1/2Na1/ 2TiO3-0.02 BiAlO3-xSrTiO3 (BNT-2BA-100xST, x = 0.20, 0.21, 0.22, 0.23, and 0.24) via analyses of the microstructure, crystal structure, dielectric, polarization, ferroelectric and electromechanical strain properties. The average grain size of BNT-2BA- 100xST ceramics decreases with increasing ST content. Results of polarization and electromechanical strain properties indicate that a ferroelectric to relaxor state transition is induced by ST modification. As a consequence, a large electromechanical strain of 592 pm/V is obtained at a relatively low electric field of 4 kV/mm in 22 mol% ST-modified BNT-2BA ceramics. We believe that the materials synthesized in this study are promising candidates for actuator applications.

산업이 발달함에 따라 이산화탄소, 휘발성 유기 화합물, 일산화탄소 등과 같은 독성 가스의 감지 및 모니터링이 중요시되고 있다. 새롭게 합성된 0 차원의 비납계 무기 페로브스카이트 소재는 광학적 방법과 전기적 방법을 융합하여 사용할 수 있는 가스 센서 특성을 가진다. 친환경 가스 센서는 결정의 상변이를 기반으로, 광학 및 전기적 특성 변화를 가져 하이드록실기 감지가 가능하며, 하이드록실기 극성과의 상관관계를 통해 차세대 센서 소자로의 응용 가능성이 기대된다.

The various sintered samples comprising of 72 wt%(Al2O3) : 28 wt%(SiO2) based ceramics were fabricated using a colloidal processing route. The phase analysis of the ceramics was performed using an X-ray diffractometer (XRD) at room temperature confirming the presence of Al2O5Si and Al5.33Si0.67O9.33. The surface morphology of the fracture surface of the different sintered samples having different sizes of grain distribution. The resistive and capacitive properties of the three different sintered samples at frequency sweep (1 kHz to 1 MHz). The contribution of grain and the non-Debye relaxation process is seen for various sintered samples in the Nyquist plot. The ferroelectric loop of the various sintered sample shows a slim shape giving rise to low remnant polarization. The excitation performance of the sample at a constant electric signal has been examined utilizing a designed electrical circuit. The above result suggests that the prepared lead-free ceramic can act as a base for designing of dielectric capacitors or resonators.

NKN [(Na,K)NbO3] is a candidate lead-free piezoelectric material to replace PZT [Pb(Zr,Ti)O3]. A single crystal has excellent piezoelectric-properties and its properties are dependent of the crystal orientation direction. However, it is hard to fabricate a single crystal with stoichiometrically stable composition due to volatilization of sodium during the growth process. To solve this problem, a solid solution composition is designed (Na,K)NbO3-Ba(Cu,Nb)O3 and solid state grain growth is studied for a sizable single crystal. Ceramic powders of (Na,K)NbO3-M(Cu,Nb)O3 (M = Ca, Sr, Ba) are synthesized and grain growth behavior is investigated for different temperatures and times. Average normal grain sizes of individual specimens, which are heat-treated at 1,125 oC for 10 h, are 6.9, 2.8, and 1.6 m for M = Ca, Sr, and Ba, respectively. Depending on M, the distortion of NKN structure can be altered. XRD results show that (NKN-CaCuN: shrunken orthorhombic; NKN-SrCuN: orthorhombic; NKN-BaCuN: cubic). For the sample heat-treated at 1,125 oC for 10 h, the maximum grain sizes of individual specimens are measured as 40, 5, and 4,000 m for M = Ca, Sr, and Ba, respectively. This abnormal grain size is related to the partial melting temperature (NKN-CaCuN: 960 oC; NKN-SrCuN: 971 oC; NKN-BaCuN: 945 oC).

A lead-free bulk ceramic having a chemical formula Ba0.8Ca0.2(Ti0.8Zr0.1Ce0.1)O3 (further termed as BCTZCO) is synthesized using mixed oxide route. The structural, dielectric, impedance, and conductivity properties, as well as the modulus of the synthesized sample are discussed in the present work. Analysis of X-ray diffraction data obtained at room temperature reveals the existence of some impurity phases. The natural surface morphology shows close packing of grains with few voids. Attempts have been made to study the (a) effect of microstructures containing grains, grain boundaries, and electrodes on impedance and capacitive characteristics, (b) relationship between properties and crystal structure, and (c) nature of the relaxation mechanism of the prepared samples. The relationship between the structure and physical properties is established. The frequency and temperature dependence of the dielectric properties reveal that this complex system has a high dielectric constant and low tangent loss. An analysis of impedance and related parameters illuminates the contributions of grains. The activation energy is determined for only the high temperature region in the temperature dependent AC conductivity graph. Deviation from the Debye behavior is seen in the Nyquist plot at different temperatures. The relaxation mechanism and the electrical transport properties in the sample are investigated with the help of various spectroscopic (i.e., dielectric, modulus, and impedance) techniques. This lead free sample will serve as a base for device engineering.

Pb(Zr,Ti)O3 (PZT) is used for the various piezoelectric devices owing to its high piezoelectric properties. However, lead (Pb), which is contained in PZT, causes various environment contaminations. (K,Na)NbO3 (NKN) is the most well-known candidate for a lead-free composition to replace PZT. A single crystal has excellent piezoelectric-properties and its properties can be changed by changing the orientation direction. It is hard to fabricate a NKN single crystal due to the sodium and potassium. Thus, (Na,K)NbO3-Ba(Cu,Nb)O3 (NKN-BCuN) is chosen to fabricate the single crystal with relative ease. NKNBCuN pellets consist of two parts, yellow single crystals and gray poly-crystals that contain copper. The area that has a large amount of copper particles may melt at low temperature but not the other areas. The liquid phase may be responsible for the abnormal grain growth in NKN-BCuN ceramics. The dielectric constant and tan δ are measured to be 684 and 0.036 at 1 kHz in NKN-BCuN, respectively. The coercive field and remnant polarization are 14 kV/cm and 20 μC/cm2.

Lead free (1-x)(0.675BiFeO3-0.325BaTiO3)- xLiTaO3 (BFBTLT, x = 0, 0.01, 0.02, and 0.03, with 0.6 mol% MnO2 and 0.4 mol% CuO) were prepared by a solid state reaction method, followed by air quenching and their crystalline phase, morphology, dielectric, ferroelectric and piezoelectric properties were explored. An X-ray diffraction study indicates that lithium (Li) and tantalum (Ta) were fully incorporated in the BFBT materials with the absence of any secondary phases. Dense ceramic samples (> 92 %) with a wide range of grain sizes from 3.70 μm to 1.82 μm were obtained in the selected compositions (0 ≤ x ≤ 0.03) of BFBTLT system. The maximum temperatures (Tmax) were mostly higher than 420 oC in the studied composition range. The maximum values of maximum polarization (Pmax ≈ 31.01 μC/cm2), remnant polarization (Prem ≈ 22.82 μC/cm2) and static piezoelectric constant (d33 ≈ 145 pC/N) were obtained at BFBT-0.01LT composition with 0.6 mol% MnO2 and 0.4 mol% CuO. This study demonstrates that the high Tmax and d33 for BFBTLT ceramics are favorable for industrial applications.

This work focuses on the electrical conduction mechanism in a lead free (Na0.5K0.5NbO3 ; NKN) ceramics system with LiNbO3 content of approximately critical concentration x ≥ 0.2. Lead free (1-x)(Na0.5K0.5)NbO3 - x(LiNbO3), NKN-LNx (x = 0.1, 0.2) ceramics were synthesized by solid-state reaction method. Crystal structures are confirmed by X-ray diffraction. The electric-mechanical bond coefficient k p decreases and the phase transition temperature T c increases with increasing x content, as determined by dielectric and piezoelectric measurements. The value of the real dielectric constants ε' and kBTε'' showed anomalies around T c (462 oC in the NKN-LN0.1 and 500 oC in the NKN-LN0.2). For the ionic conduction of mobile ions, the activation energies are obtained as EI = 1.76 eV (NKN-LN0.1) and EI = 1.55 eV (NKN-LN0.2), above T c, and EII = 0.78 (NKNLN0.1) and EII = 0.81 (NKN-LN0.2) below T c. It is believed that the conduction mechanisms of NKN-LNx ceramics are related to ionic hopping conduction, which may arise mainly due to the jumping of Li+ ions.

This study has assessed mechanical bonding strength of lead-free solder joint. Assessment methods was performing long-term reliability test about thermal shock, thermal life and high temperature & high humidity. Based on the results of analyzing mean values that was obtained from repetion of 5 times according to each conditions, reduction of mechanical bonding strength of each tests was confirmed. When it comes to HB chip, the order of high deviation rate was shown thermal shock, high temperature & humidity and thermal life. And the higher deviation rate of R0 is high temperature & humidity, thermal life and thermal shock. The order of high deviation rate of C1 chip is high temperature & humidity, thermal shock and thermal life. Related to this result of experiment, the most stable error range of mechanical bonding strength is established. From now on optimized quantity of solder and shape of solder-joint is needed by establishing a test method which can make error range of mechanical bonding strength minimize.

Bi0.5Na0.5TiO3 (BNT) based ceramics are considered potential lead-free alternatives for Pb(Zr,Ti)O3(PZT) based ceramics in various applications such as sensors, actuators and transducers. However, BNT-based ceramics have lower electromechanical performance as compared with PZT based ceramics. Therefore, in this work, lead-free bulk 0.99[(Bi0.5Na0.5)0.935Ba0.065](1-x)LaxTiO3-0.01SrZO3 (BNBTLax-SZ, with x = 0, 0.01, 0.02) ceramics were synthesized by a conventional solid state reaction The crystal structure, dielectric response, degree of diffuseness and electric-field-induced strain properties were investigated as a function of different La concentrations. All samples were crystallized into a single phase perovskite structure. The temperature dependent dielectric response of La-modified BNBT-SZ ceramics showed lower dielectric response and improved field-induced strain response. The field induced strain increased from 0.17% for pure BNBT-SZ to 0.38 % for 1 mol.% La-modified BNBT-SZ ceramics at an applied electric field of 6 kV/mm. These results show that Lamodified BNBT-SZ ceramic system is expected to be a new candidate material for lead-free electronic devices.

The effects of Nb doping on the crystal structure, microstructure, and dielectric ferroelectric and piezoelectric properties of (Bi0.5Na0.5)0.935Ba0.065Ti(1-x)NbxO3-0.01SrZrO3 (BNBTNb-SZ, with x = 0, 0.01 and 0.02) ceramics have been investigated. X-ray diffraction patterns revealed that all ceramics have a pure perovskite structure with tetragonal symmetry. The grain size of the ceramics slightly decreased and a change in grain morphology from square to spherical shape was observed in the Nb-doped samples. The maximum dielectric constant temperature (Tm) increases with increasing amount of Nb; however, ferroelectric-relaxor transition temperature (TF-R) and maximum dielectric constant (εm) values decrease gradually. Nb addition disrupted the polarization hysteresis loops of the BNBT-SZ ceramics by leading a reduction in the remnant polarization coercive field and piezoelectric constant.

New lead-free piezoelectric ceramics 0.96[{Bi0.5 (Na0.84 K0.16)0.5}1-xLax(Ti1-y Nby)O3]-0.04SrTiO3 (BNKT-ST-LN, where x = y = 0.00 ≤ (x = y) ≤ 0.015) were synthesized using the conventional solid-state reaction method. Their crystal structure, microstructure, and electrical properties were investigated as a function of the La and Nb (LN) content. The X-ray diffraction patterns revealed the formation of a single-phase perovskite structure for all the LN-modified BNKT-ST ceramics in this study. The temperature dependence of the dielectric curves showed that the maximum dielectric constant temperature (Tm) shifted towards lower temperatures and the curves became more diffuse with an increasing LN content. At the optimum composition (LN 0.005), a maximum value of remnant polarization (33 C/cm2) with a relatively low coercive field (22 kV/cm) and high piezoelectric constant (215 pC/N) was observed. These results indicate that the LN co-modified BNKT-ST ceramic system is a promising candidate for lead-free piezoelectric materials.

Studies on lead-free piezoelectrics have been attractive as means of meeting environmental requirements. We synthesized lead-free piezoelectric (Bi1/2Na1/2)TiO3-Ba(Cu1/3Nb2/3)O3 (BNT-BCN) ceramics, and their dielectric, piezoelectric, and strain behavior were characterized. As BCN with a tetragonal phase was incorporated into the rhombohedral BNT lattice, the lattice constant increased. A small amount of BCN increased the density and dielectric constant forming the complete solid solution with BNT. However, BCN above 10 mol% was precipitated into a separate phase, and which was detected with XRD. In addition, EDX measurement revealed that Cu in BCN was not distributed homogeneously but was accumulated in a certain area. A lower density with a large amount of BCN was attributed to the nonsinterable property of BCN with large tetragonaliy. The dielectric constant vs the temperature change and the strain vs the electric field indicated that the ferroelectric property of BNT was diminished and paraelectric behavior was enhanced with the BCN addition. BNT-7.5BCN showed a 0.11% unimorph strain with a 9.0 kV/mm electric field with little hysteresis.

Positive temperature coefficient of resistivity (PTCR) characteristics of (1-x)BaTiO3-x(Bi0.5K0.5)TiO3ceramics doped with Nb2O5 were investigated in order to develop the Pb-free PTC thermistor available at hightemperatures of >120oC. The PTCR characteristics appearing in the (Bi0.5Ki0.5)TiO3 (<5mol%) incorporatedBaTiO3 ceramics, which might be mainly due to Bi+3 ions substituting for Ba+2 sites. The 0.99BaTiO3-0.01(Bi0.5K0.5)TiO3 ceramics showed good PTCR characteristics of a low resistivity at room temperature (ρr) of31 Ω·cm, a high ρmax/ρmin ratio of 5.38×103, and a high resistivity temperature factor (α) of 17.8%/oC. Theaddition of Nb2O5 to 0.99BaTiO3-0.01(Bi0.5K0.5)TiO3 ceramics further improved the PTCR characteristics.Especially, 0.025mol% Nb2O5 doped 0.99BaTiO3-0.01(Bi0.5K0.5)TiO3 ceramics exhibited a significantly increasedρmax/ρmin ratio of 8.7×103 and a high α of 18.6%/oC, along with a high Tc of 148oC despite a slightly increasedρr of 39 Ω·cm.