Kyung Hoon Cho

Self-biased magnetoelectric response in three-phase laminates

This study reports the experimental observation and analysis of self-biased magnetoelectric (ME) effect in three-phase laminates. The 2–2 L-T mode laminates were fabricated by attaching nickel (Ni) plates and ME particulate composite plates having 3–0 connectivity with 0.948Na0.5K0.5NbO3–0.052LiSbO3 (NKNLS) matrix and Ni0.8Zn0.2Fe2O4 (NZF) dispersant. The presence of two types of ferromagnetic materials, Ni and NZF, results in built-in magnetic bias due to difference in their magnetic susceptibilities and coercivity. This built-in bias (Hbias) provides finite ME effect at zero applied magnetic dc field. The ME response of bending mode trilayer laminate NKNLS-NZF/Ni/NKNLS-NZF in off-resonance and on-resonance conditions was shown to be mathematical combination of the trilayers with configuration NKNLS-NZF/Ni/NKNLS-NZF and NKNLS/Ni/NKNLS representing contributions from magnetic interaction and bending strain.

Direct and converse effect in magnetoelectric laminate composites

In this letter, we analyze the direct and converse effect in laminate composites of magnetostrictive and piezoelectric materials. Our results deterministically show that direct magnetoelectric (ME) effect is maximized at antiresonance frequency while the converse ME effect is maximized at resonance frequency of the laminate composite. We explain this phenomenon by using piezoelectric constitutive equations and combining it with resonance boundary conditions. The dominant factor controlling the position of peak ME coefficient was found to be frequency dependent capacitance of piezoelectric layer. This study will provide guidance toward the development of magnetic field sensors based on direct effect and communication components based on converse effect.

High magnetic field sensitivity in Pb(Zr,Ti)O3–Pb(Mg1/3Nb2/3)O3 single crystal/Terfenol-D/Metglas magnetoelectric laminate composites

We report the magnetic field sensitivity results on five layer structure given as Metglas/Terfenol-D/PMN–PZT/Terfenol-D/Metglas, where PMN and PZT correspond to Pb(Mg1/3Nb2/3)O3 and Pb(Zr,Ti)O3, respectively. The piezoelectric constant (d33) of poled PMN–PZT was found to be 1600 pC/N with dielectric constant of 5380 at 1 kHz. The sensitivity measurements were conducted after attaching individual layers in the laminate clearly delineating the effect occurring in the response. The magnetoelectric response for this five layer structure at 1 kHz was found to be 5 V/cm Oe at dc bias field of 1000 Oe under an ac drive of 1 Oe. At 1 kHz frequency, the sensor was able to deterministically measure step changes of 500 nT while at 10 Hz we can clearly identify the sensitivity of 1 μT. These results are very promising for the cheap room-temperature magnetic field sensing technology.

Piezoelectric properties and temperature stability of Mn-doped Pb(Mg1/3Nb2/3)-PbZrO3-PbTiO3 textured ceramics

In this letter, we report the electromechanical properties of textured 0.4Pb(Mg1/3Nb2/3)O3–0.25PbZrO3–0.35PbTiO3 (PMN-PZT) composition which has relatively high rhombohedral to tetragonal (R-T) transition temperature (TR-T of 160 °C) and Curie temperature (TC of 234 °C) and explore the effect of Mn-doping on this composition. It was found that MnO2-doped textured PMN-PZT ceramics with 5 vol. % BaTiO3 template (T-5BT) exhibited inferior temperature stability. The coupling factor (k31) of T-5BT ceramic started to degrade from 75 °C while the random counterpart showed a very stable tendency up to 180 °C. This degradation was associated with the “interface region” formed in the vicinity of BT template. MnO2 doped PMN-PZT ceramics textured with 3 vol. % BT and subsequently poled at 140 °C (T-3BT140) exhibited very stable and high k31 (>0.53) in a wide temperature range from room temperature to 130 °C through reduction in the interface region volume. Further, the T-3BT140 ceramic exhibited excellent hard and so...

Self-biased converse magnetoelectric effect

In this letter, we investigate the direct magnetoelectric (DME) and converse magnetoelectric (CME) effects in three-phase metal–ceramic laminate composites. Longitudinally poled and transversely magnetized (L-T) laminate was fabricated by bonding nickel plates between the two particulate magnetoelectric (ME) composite layers of composition 0.8 (0.948 K0.5Na0.5NbO3 – 0.052 LiSbO3) – 0.2 (Ni0.8Zn0.2Fe2O4) (KNNLS-NZF). Under off-resonance condition, the laminates exhibited hysteretic DME and CME responses as a function of applied bias field (Hbias). Self-biased effect characterized by non-zero ME response at zero Hbias was observed. The self-biased DME and CME properties were found to be enhanced under resonance conditions. Without external Hbias, magnetic induction switching was possible by applying AC voltage. These results provide the possibility of using self-biased CME effect in electrically controlled memory devices and magnetic flux control devices.

Effect of intensive and extensive loss factors on the dynamic response of magnetoelectric laminates

We report the correlation between intensive and extensive losses in piezoelectric materials with the frequency dependent response of layered magnetoelectric (ME) composites. Three different piezoelectric compositions were synthesized to achieve varying loss characteristics allowing a systematic interpretation of changes in ME coupling in terms of loss components. We clearly demonstrate that intensive dielectric and piezoelectric loss play an important role in controlling the ME sensitivity of layered composites in sub-resonance low frequency range while extensive mechanical loss is dominant factor at resonance condition. Further, the maximum in ME response is obtained at antiresonance frequency of piezoelectrics.

Phase transition and temperature stability of piezoelectric properties in Mn-modified Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

This study investigates the effect of two different Mn modifiers [MnO2 and Pb(Mn1/3Nb2/3)O3(PMnN)] on the of phase transitions in Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics. The temperature dependence of polarization derived from measured pyroelectric current indicated change in nature of phase transition with MnO2 doping. This phenomenon was supported by the temperature evolution of the linear softening of low lying hard lattice mode as revealed by Raman analysis. The grain size was found to increase with MnO2 doping (5X) while decrease with PMnN modification (0.5X). Interestingly, the piezoelectric constant of MnO2 modified composition showed negligible degradation (<1%) even after heat treatment very close to the ferroelectric-paraelectric transition temperature.

Structure–performance relationships for cantilever-type piezoelectric energy harvesters

This study provides comprehensive analysis of the structure–performance relationships in cantilever-type piezoelectric energy harvesters. It provides full understanding of the effect of all the practical global control variables on the harvester performance. The control variables considered for the analysis were material parameters, areal and volumetric dimensions, and configuration of the inactive and active layers. Experimentally, the output power density of the harvester was maximum when the shape of the beam was close to a square for a constant bending stiffness and a fixed beam area. Through analytical modeling of the effective stiffness for the piezoelectric bimorph, the conditions for enhancing the bending stiffness within the same beam volume as that of a conventional bimorph were identified. The harvester configuration with beam aspect ratio of 0.86 utilizing distributed inactive layers exhibited an giant output power of 52.5 mW and power density of 28.5 mW cm−3 at 30 Hz under 6.9 m s−2 excitation. The analysis further indicates that the trend in the output power with varying damping ratio is dissimilar to that of the efficiency. In order to realize best performance, the harvester should be designed with respect to maximizing the magnitude of output power.This study provides comprehensive analysis of the structure–performance relationships in cantilever-type piezoelectric energy harvesters. It provides full understanding of the effect of all the practical global control variables on the harvester performance. The control variables considered for the analysis were material parameters, areal and volumetric dimensions, and configuration of the inactive and active layers. Experimentally, the output power density of the harvester was maximum when the shape of the beam was close to a square for a constant bending stiffness and a fixed beam area. Through analytical modeling of the effective stiffness for the piezoelectric bimorph, the conditions for enhancing the bending stiffness within the same beam volume as that of a conventional bimorph were identified. The harvester configuration with beam aspect ratio of 0.86 utilizing distributed inactive layers exhibited an giant output power of 52.5 mW and power density of 28.5 mW cm−3 at 30 Hz under 6.9 m s−2 excitatio...

Enhanced temperature stability in 〈111〉 textured tetragonal Pb(Mg1/3Nb2/3)O3-PbTiO3 piezoelectric ceramics

Two different templates (〈001〉 Ba6Ti17O40 and 〈111〉 BaTiO3) were used for synthesizing 〈111〉 textured tetragonal 0.6Pb(Mg1/3Nb2/3)O3-0.4PbTiO3(PMN-40PT) ceramics. It was found that a texture degree of 95% along 〈111〉 direction can be achieved by using only 1 vol. % 〈111〉 BaTiO3 template due to its high chemical stability in the PMN-40PT matrix. The textured PMN-40PT ceramics with tetragonal structure exhibited an excellent temperature stability of piezoelectric properties due to the absence of intermediate phase transitions between room temperature and the Curie temperature. Unlike the single crystal counterpart, the effect of 〈111〉 grain orientation in the textured PMN-40PT ceramic on enhancing the macroscopic piezoelectric response was not significant in spite of its giant local piezoresponse. We provide detailed discussions on the nature of piezoelectric response in the 〈111〉 textured tetragonal PMN-40PT ceramic with “3T” engineered domain configuration and resultant strategy to realize high performanc...

Zigzag-shaped piezoelectric based high performance magnetoelectric laminate composite

We demonstrate a 33-mode piezoelectric structure with zigzag shape for high sensitivity magnetoelectric laminates. In contrast to the 33-mode macro fiber composite (MFC), this zigzag shape piezoelectric layer excludes epoxy bonding layer between the electrode and piezoelectric materials, thereby, significantly improving the polarization degree, electromechanical coupling, and the stability of loss characteristics. The polarization degree was monitored from the change in phase angle near resonance, and the loss stability was determined from the changes in dielectric loss and rate of capacitance variation defined by (C − Cf)/Cf, where C is capacitance at a given frequency and Cf is capacitance at 100 Hz. Magnetoelectric composite with zigzag patterned piezoelectric layer was found to exhibit giant magnetoelectric response both in low frequency off-resonance region (6.75 V cm−1 Oe−1 at 1 kHz) and at anti-resonance frequency (357 V cm−1 Oe−1).