Ferroelectrics Physical Effects Part 8 ppt

B-site Multi-element Doping Effect on Electrical Property of Bismuth Titanate Ceramics 269 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 0.0 0.2 0.4 0.6 0.8 1.0 M"/M" max f/f max 300 o C 350 o C 400 o C 450 o C 500 o C 550 o C 600 o C Fig. 28. Normalized plots of electric modulus against normalized frequency at various temperatures for 8BTNTS ceramics from Debye-type relaxation. When β is close to zero, there exists a strong correlation between the hopping ions and its neighbouring ions. The β was calculated at different temperatures using the electric modulus formalism. For the ideal Debye type relaxation, the full-width half maximum (FWHM) of imaginary part of electric modulus is 1.14 decades. Therefore, β can be defined as 1.14/FWHM. One can estimate DC conductivity at different temperatures using the electrical relaxation data. The DC conductivity can be expressed as (Ngai, 1984): () () ()* () 1 o DC m T MT T ∞ ⎡ ⎤ ε ⎢⎥ β σ= ⎢ ⎥ τ Γ ⎢ ⎥ β ⎣ ⎦ (16) where o ε is the free space dielectric constant, M ∞ (T) is the reciprocal of high frequency dielectric constant and τ m (T)(1/2πf max ) is the temperature dependent relaxation time. This equation is applicable to a variety of materials with low concentrations of charge carriers (Takahashi, 2004; Vaish, 2009). Calculation for DC conductivity from AC conductivity formalism causes a large error (due to electrode effect) that can be circumvented from the electrical relaxation formalism. Fig. 27 shows the DC conductivity data obtained from the above expression (Eq. 16) at various temperatures. The activation energy for the DC conductivity was calculated from the plot of ln( σ DC ) versus 1000/T for BTNTS ceramics, which is shown in Fig. 27. The plot is found to be linear and fitted using following the Arrhenius equation, () exp DC DC E TB kT ⎛⎞ σ= − ⎜⎟ ⎝⎠ (17) where B is the pre-exponential factor and E DC is the activation energy for the DC conduction. The activation energy is calculated from the slope of the fitted line and found to be 1.08 ± 0.02 eV. This value for activation energy is in close agreement with the activation energy for Ferroelectrics – Physical Effects 270 electrical relaxation. Fig. 28 represents the normalized plots of electric modulus " M as a function of frequency wherein the frequency is scaled by the peak frequency. A perfect overlapping of all the curves on a single master curve is not found. This shows that the conduction mechanism changed with temperature which is in good agreement with that of reported in literature (Takahashi et al 2004). Takahashi et al. reported that BIT exhibits mixed (ionic-p-type) conduction at high temperature and ionic conductivity was larger than hole conductivity in Curie temperature range. 100m 1 10 100 1k 10k 100k 1M 100 1k 10k 100k 1M ε r ' f (Hz) 300 o C 350 o C 400 o C 450 o C 500 o C 550 o C 600 o C (a) 100m 1 10 100 1k 10k 100k 1M 0 20 40 60 80 tanδ f (Hz) 300 o C 350 o C 400 o C 450 o C 500 o C 550 o C 600 o C Relaxation (grain boundary) (b) Fig. 29. The frequency dependence of (a) the dielectric constant and (b) loss at various temperatures for 8BTNTS ceramics Fig. 29 shows the frequency dependence plots of permittivity (ε’) and dielectric loss (tanδ) at various temperatures for 8BTNTS ceramics. It is evident that at all the temperatures (Fig. 29 (a)), the value of ε’ decreases with increasing frequency and attains a constant value. The high value of the dielectric constant in low-frequency regions is a extrinsic phenomenon arising due to the presence of metallic or blocking electrodes which do not permit the mobile ions to transfer into the external circuit, and as a result, mobile ions pile up near the B-site Multi-element Doping Effect on Electrical Property of Bismuth Titanate Ceramics 271 electrodes and give a large bulk polarization in the materials as well as oxygen ion polarization at grain boundaries. When the temperature rises, the dispersion region shifts towards higher frequencies and the nature of the dispersion changes at low frequencies due to the electrode polarization along with grain boundary effects. A plateau region at 500 °C was observed at moderately low frequencies that shifted to higher frequencies with increase in temperature (600 °C). This plateau region distinguished electrode polarizations to the grain boundary polarizations. The variation in the tanδ with the temperature at various frequencies (Fig. 29(b)) is consistent with that of the dielectric behaviour. The loss decreases with increase in frequency at different temperatures (300-600 °C). It is also observed that the dielectric loss increases with increase in temperature which is attributed to the increase in conductivity of the ceramics due to thermal activation of conducting species. The clear relaxation peak was not encountered at any temperature under study because of dominant DC conduction losses due to high oxygen ion mobility in the temperature range under study. 5. Conclusions We have reported the effects of composition and crystal lattice structure upon microstructure, dielectric, piezoelectric and electrical properties of BIT, Bi 4 Ti 3- x W x O 12+x +0.2wt%Cr 2 O 3 (BTWC), Bi 4 Ti 3-2x Nb x Ta x O 12 (BTNT) and Bi 4 Ti 3-2x Nb x Ta x-y Sb y O 12 (BTNTS) ceramics. WE have shown how doping can increase the piezoelectric coefficient of BIT. For the W/Cr samples, a d 33 coefficient of 22 pC N -1 was measured for x=0.025. The piezoelectric coefficient d 33 of Bi 4 Ti 2.98 Nb 0.01 Ta 0.01 O 12 ceramics controlled by precisely optimizing Nb/Ta amounts is found to be 26 pC N -1 . The highest room temperature value of the piezoelectric coefficient is found to be 35 pC N -1 for 8BTNTS ceramics. The antimony incorporation into the BTNT ceramics controlled electrical conductivity through reduction in the ionic and electronic conductivities as well as altered microstructure. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 1.0 ± 0.03 eV, close to that of the activation energy for DC conductivity (1.08 ± 0.02 eV). It suggests that the movements of oxygen ions are responsible for both ionic conduction as well as the relaxation process. These results demonstrated that 8BTNTS ceramic is a promising candidate for high temperature piezoelectric applications. 6. 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(2006) Doping Effects on the Electrical Condcutivity of Bismuth Layered Bi 3 TiNbO 9 -based Ceramics. J. Appl. Phys., 100, 044112. Zhang, Q.; Zhang, B.; Li, H.; et al. (2010) Effects of Sb content on electrical properties of lead-free piezoelectric [(Na 0.535 K 0.480 ) 0.942 Li 0.058 ](Nb 1−x Sb x )O 3 ceramics J. Ally. Compd., 490, 260. Part 3 Magnetoelectrics and Multiferroics 12 Magnetoelectric Multiferroic Composites M. I. Bichurin 1 , V. M. Petrov 1 and S.Priya 2 1 Novgorod State University 2 Virginia Tech 1 Russia 2 USA 1. Introduction Magnetoelectric (ME) multiferroics are materials in which ferromagnetism and ferroelectricity occur simultaneously and coupling between the two is enabled. Applied magnetic field H gives rise to an induced polarization P which can be expressed in terms of magnetic field by the expression, P=αH, where α is the ME-susceptibility tensor. Most of the known single-phase ME materials are known to show a weak ME coupling (Fiebig, 2005; Kita et al., 1988; Wang et al., 2003; Prellier et al., 2005; Cheong et al., 2007). A composite of piezomagnetic and piezoelectric phases is expected to have relatively strong ME coupling. ME interaction in a composite manifests itself as inducing the electrical voltage across the sample in an applied ac magnetic field and arises due to combination of magnetostriction in magnetic phase and piezoelectricity in piezoelectric phase through mechanical coupling between the components (Ryu et al., 2001; Nan et al., 2008; Dong et al., 2003; Cai et al., 2004; Srinivasan et al., 2002). In last few years, strong magneto-elastic and elasto-electric coupling has been achieved through optimization of material properties and proper design of transducer structures. Lead zirconate titanate (PZT)-ferrite and PZT-Terfenol-D are the most studied composites to-date (Dong et al., 2005; Dong et al.,2006b; Zheng et al., 2004a; Zheng et al., 2004b). One of largest ME voltage coefficient of 500 Vcm -1 Oe -1 was reported recently for a high permeability magnetostrictive piezofiber laminate (Nan et al., 2005; Liu et al., 2005). These developments have led to magnetoelectric structures that provide high sensitivity over a varying range of frequency and DC bias fields enabling the possibility of practical applications. In this paper, we focus on four broad objectives. First, we discuss detailed mathematical modeling approaches that are used to describe the dynamic behavior of ME coupling in magnetostrictive-piezoelectric multiferroics at low-frequencies and in electromechanical resonance (EMR) region. Expressions for ME coefficients were obtained using the solution of elastostatic/elastodynamic and electrostatic/magnetostatic equations. The ME voltage coefficients were estimated from the known material parameters. The basic methods developed for decreasing the resonance frequencies were analyzed. The second type of resonance phenomena occurs in the magnetic phase of the magnetoelectric composite at much higher frequencies, called as ferromagnetic resonance (FMR). The estimates for electric field induced shift of magnetic resonance line were derived and analyzed for Ferroelectrics – Physical Effect 278 varying boundary conditions. Our theory predicts an enhancement of ME effect that arises from interaction between elastic modes and the uniform precession spin-wave mode. The peak ME voltage coefficient occurs at the merging point of acoustic resonance and FMR frequencies. Second, we present the experimental results on lead – free magnetostrictive –piezoelectric composites. These newly developed composites address the important environmental concern of current times, i.e., elimination of the toxic “lead” from the consumer devices. A systematic study is presented towards selection and design of the individual phases for the composite. Third, experimental data from wide range of measurement and literature was used to validate the theoretical models over a wide frequency range. Lastly, the feasibility for creating new class of functional devices based on ME interactions is addressed. Appropriate choice of individual phases with high magnetostriction and piezoelectricity will allow reaching the desired magnitude of ME coupling as deemed necessary for engineering applications over a wide bandwidth including the electromechanical, magnetoacoustic and ferromagnetic resonance regimes. Possibilities for application of ME composites in fabricating ac magnetic field sensors, current sensors, transformers, and gyrators are discussed. ME multiferroics are shown to be of interest for applications such as electrically-tunable microwave phase-shifters, devices based on FMR, magnetic-controlled electro-optical and piezoelectric devices, and electrically-readable magnetic memories. 2. Low-frequency magnetoelectric effect in magnetostrictive-piezoelectric bilayers We consider only (symmetric) extensional deformation in this model and at first ignore any (asymmetric) flexural deformations of the layers that would lead to a position dependent elastic constants and the need for perturbation procedures. For the polarized piezoelectric phase with the symmetry m, the following equations can be written for the strain and electric displacement:   ; ; ppppp iijjkik ppppp kkiiknn SsTdE DdT E   (1) where p S i and p T j are strain and stress tensor components of the piezoelectric phase, p E k and p D k are the vector components of electric field and electric displacement, p s ij and p d ki are compliance and piezoelectric coefficients, and p ε kn is the permittivity matrix. The magnetostrictive phase is assumed to have a cubic symmetry and is described by the equations:  ; ; mmmmm iijjkik mmmmm kkiiknn SsTqH BqT H   (2) where m S i and m T j are strain and stress tensor components of the magnetostrictive phase, m H k and m B k are the vector components of magnetic field and magnetic induction, m s ij and m q ki are compliance and piezomagnetic coefficients, and m μ kn is the permeability matrix. Equation (2) may be considered in particular as a linearized equation describing the effect of [...]... Letters V 89 , Issue 25 (December 2006), p.p 252904 (1-3), ISSN 107731 18 Fetisov, Y.K., Petrov, V.M., & Srinivasan, G (2007) Inverse magnetoelectric effects in a ferromagnetic–piezoelectric layered structure, Journal of Materials Research V 22, Number 8 (August 2007) p.p 2074-2 080 ISSN: 088 4-2914 Fiebig, M (2005) Revival of the magnetoelectric effect Journal of physics D, Applied physics, Vol 38, Issue 8 (April... alloys, and polymers, Applied Physics Letters V 84 , Number 18 (May 2004) p.p 3516-35 18, ISSN 1077-31 18 Chashin, D.V., Fetisov, Y.K., Kamentsev, K.E., & Srinivasan, G (20 08) Resonance magnetoelectric interactions due to bending modes in a nickel-lead zirconate titanate bilayer, Appl Phys Lett V 92, Issue 10 (March 20 08) , p.p 102511 (1-3), ISSN 1077-31 18 Cheong, S W & Mostovoy, (2007) M Multiferroics:... magnetostrictive-piezoelectric bilayers, Physical Review B, V 68, Issue 5 (August 2003), p.p 054402 (1-13), ISSN 1550-235X Bichurin, M.I., Filippov, D.A., Petrov, V.M., Laletsin, V.M., Paddubnaya N., & Srinivasan, G (2003b) Resonance magnetoelectric effects in layered magnetostrictive-piezoelectric composites, Phys Rev.B 68, Physical Review B, V 68, Issue 13 (October 2003), p.p 1324 08 (1-4) , ISSN 1550-235X Bichurin,... Terfenol-D/steel/Pb(Zr,Ti)O3 magnetoelectric laminate composites Appl Phys Lett V 89 , Issue 11 (September 2006), pp 112911 (1-3), ISSN 1077-31 18 Yang, S.-C., Ahn, C.-W., Park, C.-S., & Priya, S (2011) Synthesis and characterization of leadfree 0 .8 [0.948K0.5Na0.5NbO3 – 0.052LiSbO3] – 0.2 Ni0.8Zn0.2Fe2O4 (KNNLS-NZF) 302 Ferroelectrics – Physical Effect island - matrix magnetoelectric composites and their application... (Li,Na)NbO3 ceramics, Proceedings of International Conference on Ferroelectrics, Nara, Japan, 2002 Kita, E., Takano, S., Tasaki, A., Siratori, K., Kohn, K., & Kimura, S (1 988 ) Low-temperature phase of yttrium iron garnet (YIG) and its first-order magnetoelectric effect, Journal of Applied Physics, Vol 64, Issue 10 (November 1 988 ), p.p 5659-5661, ISSN 1 089 7550 Kornev, I., Bichurin, M., Rivera, J.-P., Gentil,... (20 08) , Multiferroic magnetoelectric composites: Historical perspective, status, and future directions, Journal of Applied Physics, Vol 103, (February 20 08) , p.p 031101 (1-35), ISSN 1 089 7550 Osaretin, Idahosa A & Rojas, Roberto G (2010) Theoretical model for the magnetoelectric effect in magnetostrictive/piezoelectric composites, Physical Review B, V 82 , Issue 17 (Novenber 2010), p.p 174415 (1 -8) ,... (pC/N) kp 3T/0 Qm Tc (oC) Sin T (oC) None 40,41 225 0.36 1,0 58 74 320 1,060 0.5 mol% MnO2 53 237 0.42 1,252 92 294 1,050 1.0 mol% ZnO 220 0.36 1,1 38 71 - 1,040 2.0 mol% CuO 47,54 220 0.34 1, 282 186 286 950 2.0 mol% CuO + 0.5 mol% MnO2 54 2 48 0.41 1,2 58 305 277 950 Table 3 Piezoelectric and dielectric properties of 0.95(Na0.5K0.5)-0.05BaTiO3 + additives Fig 10 Comparison of magnetic properties for... understanding of ME effects and for useful technologies In a composite, the interaction between electric and magnetic subsystems can be expressed in terms of a ME susceptibility In general, the susceptibility is defined by the following equations for the microwave region (Kornev et al., 2000; Bichurin, 1994; Bichurin et al., 1990) p  Ee  EM h , m  MEe  M h ( 18) 286 Ferroelectrics – Physical Effect... titanate volume, attains a peak value for v = 0.5 and then drops with increasing v as in Fig 1 ME voltage coefficient (V/cm Oe) 160 120 80 40 0 240 250 260 Frequency (kHz) 270 Fig 1 Frequency dependence of αE,13 for the bilayer with v=0.5 280 282 Ferroelectrics – Physical Effect 4 ME effect at bending modes of EMR A key drawback for ME effect at longitudinal modes is that the frequencies are quite... coefficient, Applied Physics Letters V 87 , Issue 6 (August 2005), p.p 062502 (1-3), ISSN 1077-31 18 Dong, S X., Zhai, J Y., Li, J F., Viehland, D., & Bichurin, M I (2006a) Magnetoelectric gyration effect in Tb1−xDyxFe2−y/Pb(Zr,Ti)O3 laminated composites at the electromechanical resonance, Applied Physics Letters V 89 , Issue 24 (December 2006) p.p 243512 (1-3) , ISSN 1077-31 18 Dong, S., Zhai, J., Li, J., & . to be 1. 08 ± 0.02 eV. This value for activation energy is in close agreement with the activation energy for Ferroelectrics – Physical Effects 270 electrical relaxation. Fig. 28 represents. Solid Solutions. Phys. Rev. 122, 80 4. Saito, Y.; Takao, H.; Tani, T.; et al. (2004) Lead-free piezoceramics. Nature, 432, 84 . Ferroelectrics – Physical Effects 274 Shimakawa, Y.; Kubo,. 0 40 80 120 160 240 250 260 270 280 Frequenc y ( kHz ) ME voltage coefficient (V/cm Oe) Fig. 1. Frequency dependence of α E,13 for the bilayer with v=0.5 Ferroelectrics – Physical