Woon-Ha Yoon

Mechanical and in vitro biological performances of hydroxyapatite-carbon nanotube composite coatings deposited on Ti by aerosol deposition.

Hydroxyapatite (HA)-carbon nanotube (CNT) composite coatings on Ti plate, produced by aerosol deposition using HA-CNT powders, were developed for biomedical applications. For the deposition process HA-CNT powder mixtures with CNT contents of 1 and 3 wt.% were used. Dense coatings with a thickness of 5 microm were fabricated, irrespective of the content of CNTs. No pores or microcracks were observed in the coatings. The coatings had good adhesion to the substrate, exhibiting a high adhesion strength, ranging from 27.3 to 29.0 MPa. Microstructural observation using field-emission gun scanning electron microscopy and transmission electron microscopy showed that CNTs with a typical tubular structure were found in the HA-CNT composite coatings. Nanoindentation tests revealed that the mechanical properties, such as the hardness and elastic modulus, were significantly improved by the addition of the CNTs to the HA coating. In addition, the proliferation and alkaline phosphatase (ALP) activity of MC3T3-E1 pre-osteoblast cells grown on the HA-CNT composite coatings were higher than those on the bare Ti and pure HA coating. The ALP activity of the composite coatings considerably improved as the CNT content increased. These results suggest that CNTs would be an effective reinforcing agent to enhance both the mechanical and biological performances of HA coatings.

Fabrication and ferroelectric properties of highly dense lead-free piezoelectric (K0.5Na0.5)NbO3 thick films by aerosol deposition

Lead-free piezoelectric thick films of (K0.5Na0.5)NbO3 were fabricated by aerosol-deposition method. The thickness of KNN film was 7.1μm and fully dense films were obtained. The dielectric constants e3T∕e0 of the as-deposited and annealed films at 1kHz were 116 and 545, respectively, which are higher than any previously reported values for lead-free piezoelectric thin/thick films, either without or with heat treatment. The ferroelectric properties were improved after annealing and the maximum values of Pr=8.1μC∕cm3 and Ec=100kV∕cm were achieved. These values are markedly superior to those of sintered KNN ceramic counterparts.

Ferroelectric and piezoelectric properties of 0.948(K0.5Na0.5)NbO3–0.052LiSbO3 lead-free piezoelectric thick film by aerosol deposition

Lead-free, piezoelectric thick films of 0.948(K0.5Na0.5)NbO3–0.052LiSbO3 were fabricated by aerosol deposition and the effect of postannealing temperature on the dielectric, ferroelectric, and piezoelectric properties was investigated. The thickness of the films ranged from 5to17μm and highly dense films were obtained after deposition at room temperature. With increasing annealing temperature, the dielectric and ferroelectric properties were markedly increased. The maximum ferroelectric and dielectric properties of e3T∕e0=1012, Pr=15.5μC∕cm2, and d33=50pm∕V were obtained after annealing at 800°C for 1h. Above this temperature, the film exhibited rapid property degradation as it was decomposed due to Na2O evaporation.

Multiple broadband magnetoelectric response in thickness-controlled Ni/[011] Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 single crystal/Ni laminates

We report the realization of a multiple, broadband, magnetoelectric (ME) response using Ni/[011]-Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 (PMN-PZT) single crystal/Ni laminates that take advantage of the multiple mechanical resonances inherent to laminates with anisotropic piezoelectric properties. The ME voltage coefficient of the laminates showed three distinct resonance frequencies and large in-plane anisotropy in its sign and magnitude owing to the anisotropic planar piezoelectric coefficient of [011]-oriented PMN-PZT single crystals. Upon serially connecting three such laminates with different thickness ratios between the Ni and PMN-PZT layers, we observed two distinct frequency windows with bandwidths of ∼60 kHz showing flat, giant ME responses of over 16 V/cm Oe, which suggests that these ME laminates are good candidates for application in broadband field sensors or energy harvesters.

Effects of Pb(Zn1∕3Nb2∕3)O3 addition and postannealing temperature on the electrical properties of Pb(ZrxTi1−x)O3 thick films prepared by aerosol deposition method

Effects of the lead zinc niobate (PZN) addition and postannealing temperature on the electrical properties of the lead zirconate titanate (PZT) films were observed to improve electrical properties of the PZT film. The PZN content was varied from 0% to 40%, and the postannealing temperature was varied from 500to900°C. The as-deposited film had a fairly dense microstructure without any cracking and showed a single perovskite phase formed with nanosized grains. Meanwhile, rapid grain growth was observed when the postannealing temperature was increased from 700to900°C. The PZN-added PZT film showed poorer electrical properties than the pure PZT film did when the films were annealed at 700°C but higher remnant polarization, dielectric constant, and piezoelectric response when the films were annealed at 900°C. Remnant polarization value, relative dielectric constant, and piezoelectric constant of the 20% PZN-added PZT films annealed at 900°C were 50.0μC∕cm2, 1643, and 200pC∕N, respectively, which are values suf...

Magnetoelectric properties and magnetomechanical energy harvesting from stray vibration and electromagnetic wave by Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 single crystal/Ni cantilever

Magnetoelectric (ME) rectangular unimorph cantilever beam structures of piezoelectric Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 (PMN-PZT) single crystal on magnetostrictive Ni plate was designed with ⟨001⟩ and ⟨011⟩-cut crystallographic directions and investigated their ME response and mechanical vibration based energy harvesting behavior. Both magnetoelectric (ME) voltage coefficient (αME) and mechanically harvested power output was found to be strongly dependent on the crystallographic cut directions of PMN-PZT single crystals. The maximum αME and power output of 7.28 V/cm Oe and 1.31 mW was observed for ⟨011⟩ PMN-PZT/i unimorph ME structure at resonance mode under 0.7 G acceleration. The ⟨011⟩ PMN-PZT single crystal showed that in-plane anisotropic behavior, i.e., d31 and d32 significantly affect to the magnitude of αME and harvested power output.

Enhancement of resonant and non-resonant magnetoelectric coupling in multiferroic laminates with anisotropic piezoelectric properties

Giant transverse magnetoelectric voltage coefficients |αE| = 751 and 305 V/cmOe at two electromechanical antiresonance frequencies are found in the symmetric metglas/[011]-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 crystal/metglas laminate. Unique torsional and diagonal vibration modes are identified to be responsible for those giant |αE| values. Moreover, αE is found to be anisotropic depending on the in-plane magnetic field directions, making the piezoelectrics with anisotropic planar piezoelectricity potentially useful base materials for multi-frequency, phase-sensitive magnetoelectric devices.

Sintering and piezoelectric properties of KNN ceramics doped with KZT

This paper investigates the effect of K_1.94 Zn_1.06Ta_5.19O₁₅ (KZT) addition on the sintering behavior and piezoelectric properties in lead-free piezoelectric ceramics of (K_0.5Na_0.5)NbO₃ (KNN). The apparent density of sintered KNN ceramics was increased with KZT addition, and a relative density of above 96.3% was obtained with the doping of over 0.5 mol% KZT. The maximum dielectric and piezoelectric properties of epsiv₃ ^T/epsiv₀ = 590, d₃₃ = 126 pC/N, k_p = 0.42, and P_tau, = 18 muC/cm² were obtained from 0.5 mol% KZT-doped KNN ceramics. A small amount of KZT (~0.5 mol%) was effective for improving the sintering behavior and piezoelectric properties, but KZT addition exceeding 1.0 mol% was effective only for den-siflcation. A small amount of KZT was effective for den-siflcation of KNN ceramics by promoting K_5.75Nb_10.8O₃₀ liquid phase formation. However, even though KNN with 1.0~2.0 mol% KZT had a relative density of > 98.5%, the piezoelectric properties were inferior to those of 0.5 mol% KZT-doped KNN, presumably due to the smaller grain size and excess liquid phase of the KNN ceramics doped with higher amounts of KZT. It is believed that a small amount of KZT could be one of the suitable sintering aids to obtain highly dense KNN based piezoelectric.

Effects of Zr/Ti ratio and post-annealing temperature on the electrical properties of lead zirconate titanate (PZT) thick films fabricated by aerosol deposition

The effects of the Zr/Ti ratio on the electrical properties of lead zirconate titanate (PZT) thick films prepared by the aerosol deposition (AD) process were investigated to optimize the electrical properties of the thick film. The Zr/Ti ratio was varied among 45/55, 52/48, and 60/40, and the post-annealing temperature was varied from 500 to 900 °C. Microscopic examination of the as-deposited films revealed crack-free and dense microstructures with a thickness of 10 μm. The annealed films showed markedly improved electrical properties in comparison with the as-deposited films with increasing post-annealing temperature. With increasing Zr/Ti ratio, the remnant polarization and coercive field decreased. The dielectric constant and piezoelectric coefficient, d 33 , were highest for the PZT 52/48 film. This film annealed at 900 °C exhibited the best overall combination of electrical properties, with a dielectric constant, remnant polarization, and piezoelectric coefficient of 1320, 31.1 μC/cm 2 , and 150 pC/N, respectively.

Fabrication of Lead Zirconate Titanate Thick Films Using a Powder Containing Organic Residue

Crack-free, lead zirconate titanate (PZT) films with a thickness range of 20–100 µm were deposited on silicon substrate by aerosol deposition (AD) process using powders containing 1–12 wt % of organic species prepared by sol–gel route. The as-deposited films were annealed at 700 °C for 5 min by rapid thermal annealing (RTA) to improve the electrical properties. No delaminations or cracks were observed in the annealed film, even for a 100-µm-thick film. The organic species was evaporated during the post-annealing process and generated nano-sized pores which seemed to alleviate the residual compressive stress. Furthermore, a high deposition rate of about 3.3 µm/s was achieved on the film area of 5 ×12 mm2 due to the incorporation of organic residue. The dielectric constant (er), remnant polarization (Pr), and piezoelectric coefficient (d33) of the 20-µm-thick PZT film were 850, 24.0 µC/cm2, and 70 pC/N, respectively, after annealing at 700 °C for 5 min.