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Dielectric behaviour and magnetoelectric effect in copper–cobalt ferrite+barium lead titanate composites
Materials Chemistry and Physics 77 (2002) 691–696
Dielectric behaviour and magnetoelectric effect in copper–cobalt ferrite + barium lead titanate composites M.B. Kothale a , K.K. Patankar b , S.L. Kadam b , V.L. Mathe b , A.V. Rao b , B.K. Chougule b,∗ b
a KLE Society’s GIB College, Nipani 591237, Karnataka, India Composite Materials Laboratory, Department of Physics, Shivaji University, Kolhapur 416004, Maharashtra, India
Received 21 November 2001; received in revised form 2 January 2002; accepted 16 February 2002
Abstract ME composites of Cu0.6 Co0.4 Fe2 O4 +Ba0.8 Pb0.2 TiO3 were prepared using a conventional ceramic double sintering process. The presence of phases was confirmed by X-ray diffraction (XRD). The variation of dielectric constant (ε ) in the frequency range 100 Hz–1 MHz and also with temperature at constant frequency was studied. The conduction phenomenon is explained on the basis of small polaron hopping model. The confirmation of this phenomenon is made with the help of AC conductivity measurements. The static value of magnetoelectric conversion factor that is dc(ME)H was studied as a function of intensity of the magnetic field. The maximum value of ME coefficient was observed for 15% ferrite + 85% ferroelectric phase. © 2002 Elsevier Science B.V. All rights reserved. Keywords: ME composites; Polaron hopping; Dielectric behaviour; Magnetoelectric effect
1. Introduction Ferrite-ferroelectric composites consist of two phases viz. piezomagnetic and piezoelectric. The magnetoelectric effect is a coupled, two field effect in which the application of electric field induces magnetization and magnetic field induces electric polarization [1]. It is due to the strain induced in the piezomagnetic/ferrite phase by the applied magnetic field, being mechanically coupled to stress induced in the piezoelectric/ferroelectric phase, the coupling resulting in an electric voltage [2,3]. The ME composites have been exploited as sensors, waveguides, switches, phase invertors, modulators, etc. [4]. ME composites also find a lot of technological applications in radioelectronics, optoelectronics, microwave electronics and transducers in instrumentation. The selection of suitable combination of piezoelectric and piezomagnetic material with a view to achieve ME effect itself is however a challenging task. In order to achieve better ME effect, the piezomagnetic coefficient of ferrite phase and the piezoelectric coefficient of ferroelectric phase must be high. The resistivity of both the phases is comparable and the mechanical coupling between the two phases is perfect [5]. The work reported in the literature is confined to measurement of ME effect in the composites containing a ferroelectric as the first ∗ Corresponding author. Tel.: +91-0231-690571; fax: +91-0231-691533.
component and Ni, Co, Mn ferrites [6,7] as the second component. In the present case copper–cobalt ferrite has been chosen with a view to introduce large Jahn–Teller distortion in the ferrite lattice which will in turn induce more mechanical coupling between the ferroelectric and ferrite phases and may yield maximum ME signal. Hence we report here our results on the measurements of dielectric constant (ε ), loss tangent (tan δ), AC conductivity and ME effect in case of Cu0.6 Co0.4 Fe2 O4 –Ba0.8 Pb0.2 TiO3 composites. These measurements throw some light on the conduction mechanism and ME conversion factor.
2. Preparation of ME composites The ME composites were prepared by normal solid state reaction. The ferrite phase viz. Cu0.6 Co0.4 Fe2 O4 was prepared through solid state reaction using CuO, CoCO3 and Fe2 O3 powders in stoichiometric proportions. The ferroelectric phase viz. Ba0.8 Pb0.2 TiO3 was prepared with BaO, PbO and TiO2 as starting materials. The ferrite powder was presintered at 700 ◦ C for 12 h and ferroelectric at 800 ◦ C for 4 h. After presintering, the constituent phases were thoroughly mixed and ground to fine powder. The ME composites were prepared by mixing 15, 30 and 45% of ferrite phase with 85, 70 and 55% ferroelectric phase respectively. They were presintered at 900 ◦ C for 12 h. The pellets of
0254-0584/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 4 - 0 5 8 4 ( 0 2 ) 0 0 1 3 5 - 9
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M.B. Kothale et al. / Materials Chemistry and Physics 77 (2002) 691–696
the composite were finally sintered at 1050 ◦ C for 24 h and furnace cooled.
3. Experimental details The composites were characterized by using X-ray diffractometer (Phillips Model PW 1710) using Cu K␣ radiation. The X-ray diffraction (XRD) pattern of the composite phase containing 30% Cu0.6 Co0.4 Fe2 O4 + 70% Ba0.8 Pb0.2 TiO3 is shown in Fig. 1. From the figure it is revealed that both the ferrite as well as ferroelectric phases are present. No irregular peaks have been found in the pattern which confirms single phase formation of composites. Lattice parameters for both the phases have been calculated. Ferrite phase has a cubic spinel structure and ferroelectric phase has a tetragonal perovskite structure. The lattice parameter for ferrite phase in the 30% ferrite composite is 8.28 Å. The lattice parameters for ferroelectric phase in 70% ferroelectric composite are a = 3.877 and c = 3.964 Å and c/a ratio equal to 1.022. The palletized samples were coated with silver paste to ensure good electric contacts. Dielectric measurements were carried out using LCR meter (Model HP 4284A) in conjunction with laboratory designed cell. The dielectric constant
was calculated by using the formula ε =
Cd ε0 A
(1)
where C is the capacitance of pellet in farad, d the thickness of the pellet and A the area of the pellet. The variation of dielectric constant for different frequencies as well as at different temperatures was studied along with the variation of AC conductivity with frequency. To obtain ME signal the palletized samples were poled electrically. For electric poling the samples were heated above their ferroelectric transition temperature in applied high electric field (2 kV cm−1 ) and then allowed to cool slowly in the field. Magnetic poling was carried out by keeping the dc magnetic field for 30 min in the saturation field of 1.5 kOe at room temperature. The electric field (E) developed at different dc field (H) was measured. From the measurements dE/dH for different values of H were calculated.
4. Results and discussion The variation of dielectric constant (ε ) with frequency for the composite xBa0.8 Pb0.2 TiO3 –(1 − x)Cu0.6 Co0.4 Fe2 O4 is shown in Fig. 2. An examination of the figure reveals the
Fig. 1. XRD pattern of 30% Cu0.6 Co0.4 Fe2 O4 –70% Ba0.8 Pb0.2 TiO3 composite.
M.B. Kothale et al. / Materials Chemistry and Physics 77 (2002) 691–696
693
Fig. 2. Variation of dielectric constant with frequency for the composite system: xBa0.8 Pb0.2 TiO3 –(1 − x)Cu0.6 Co0.4 Fe2 O4 .
dielectric dispersion. The ε rapidly decreases at lower frequencies and remains fairly constant at higher frequencies. The large values of dielectric constant at low frequencies is due to dislocations and other defects [8,9]. In case of ferrites and ferroelectric materials this large value of ε has been attributed to the effect of heterogeneity of the samples like pores and layered structure. However, in case of composites it is ascribed to the fact that ferroelectric regions are surrounded by non-ferroelectric regions similar
to the relaxor ferroelectric materials [10]. This gives rise to interfacial polarization which is reflected by sharp fall in ε . Polaron hopping mechanism resulting in electronic polarization also contributes to low frequency dispersion. The static value of dielectric constant in the present samples lies in the range 200–800 and is almost frequency independent. It is further observed that the value of ε increases with increase in ferroelectric content. The variation of tan δ with frequency shows similar behaviour.
Fig. 3. Variation of dielectric constant with temperature for the composite: 70% Ba0.8 Pb0.2 TiO3 –30% Cu0.6 Co0.4 Fe2 O4 .
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M.B. Kothale et al. / Materials Chemistry and Physics 77 (2002) 691–696
Table 1 Electrical data of xBa0.8 Pb0.2 TiO3 –(1 − x)Cu0.6 Co0.4 Fe2 O4 composites Composition
ε RT
εmax
Tc (K)
γ
α RT (V K−1 )
x x x x
677 1900 1720 1000
1250 2700 3700 2480
455 425 420 415
1.21 1.51 1.63 1.41
400 720 820 960
=1 = 0.85 = 0.7 = 0.55
The variation of dielectric constant (ε ) with temperature is shown in Fig. 3. From the figure it is revealed that ε increases with temperature upto Curie temperature (Tc ) and then it decreases. It is observed from the figure that region around dielectric peak was broadened at all frequencies. The broadening of the peak may be due to microscopic heterogeneity in the composites [5]. The transition is diffused type. In the paraelectric region ε in these composites obeys the relation [10] 1 (T − Tc )2 1 = + ε max 2γ ε max ε
(2)
where γ is the diffusivity parameter, a measure of broadness of the peak in diffused phase type behaviour (DPT). The value of γ for the present system lies between 1 and 2. This parameter varies between 1 for normal Curie–Weiss type and 2 for typical DPT type [11]. The values of ε , Curie temperature, diffusivity parameter and Seebeck coefficient are reported in Table 1 for all the composites. From Table 1 it can be seen that the Curie temperature decreases as the ferroelectric content decreases. This may be due to the statistical fluctuations in compositions in these microregions. Further, the thermoelectric power (α) increases with decrease in ferroelectric content, which may be due to the localized electronic state for the oxides [12]. The variation
of tan δ with temperature at 1 kHz is shown in Fig. 4. This behaviour is similar to the behaviour of ε versus temperature. Here also the peaks become broad near Curie temperature which indicates DPT type behaviour. In order to understand mechanism of conduction AC conductivity was measured as a function of frequency in the range 100 Hz–1 MHz at room temperature. AC conductivity obeys the following relation: σAC = Aω
(3)
where ω is the angular frequency. Fig. 5 indicates that AC conductivity (σ AC ) increases with increase in frequency. Similar results were obtained by other workers [9,13,14]. Frequency dependence of AC conductivity indicates that conduction occurs by hopping of charge carriers among localized states. The conduction is due to small polarons. The variation of magnetoelectric output (dE/dH) versus magnetic field (H) is shown in Fig. 6. For the present system ME output is found to be maximum for 85% ferroelectric + 15% ferrite composite. The dE/dH remains constant for lower magnetic field but at higher magnetic fields it decreases. The constant value of magnetoelectric conversion factor indicates magnetostriction reached its saturation value at the time of magnetic poling. In the present system appearance of ME signal is due to the strain induced by lattice distortion in the ferrite phase by Jahn–Teller ions like Cu. Hence Jahn–Teller effect in the ferrite can lead to polarization in the piezoelectric phase. After a certain field (1.9 kOe), the magnetostriction and strain produced would produce a constant electric field in the piezoelectric phase. Due to this constant field E there is decrease in dE/dH at higher magnetic fields. Further it is observed that the similar trend of variation is observed for all the three composites. As the ferrite content increases the ME output decreases.
Fig. 4. Variation of loss tangent with temperature for the composite: 70% Ba0.8 Pb0.2 TiO3 –30% Cu0.6 Co0.4 Fe2 O4 .
M.B. Kothale et al. / Materials Chemistry and Physics 77 (2002) 691–696
695
Fig. 5. Variation of AC conductivity with angular frequency for the composite system: xBa0.8 Pb0.2 TiO3 –(1 − x)Cu0.6 Co0.4 Fe2 O4 .
Fig. 6. Variation of static magnetoelectric conversion factor with magnetic field for the composite system: xBa0.8 Pb0.2 TiO3 –(1 − x)Cu0.6 Co0.4 Fe2 O4 .
5. Conclusions The XRD patterns of these composites reveals the presence of both ferrite and ferroelectric phases. The number of peaks corresponding to ferrite phase increases with increase in mol% of ferrite. The dielectric behaviour suggests the dielectric dispersion at lower frequencies. This is due to the interfacial polarization and also due to the heterogeneity of the samples. The variation of dielectric constant with temperature gives the broad maximum near the Curie temperature. This suggests DPT type behaviour similar to relaxor ferroelectrics. The variation of AC conductivity with frequency is linear in nature suggesting that the conduction is due to polaron hopping. The magnetoelectric conversion factor (dE/dH) for all the three composites is due to the strain
induced by the lattice distortion in ferrite and also magnetostriction produced due to the applied magnetic field.
Acknowledgements Authors are very thankful to late Prof. S.A. Patil, Ex-Head, Department of Physics for his constant encouragement and help throughout this work.
References [1] C.-W. Nan, Phys. Rev. B 50 (1994) 6082. [2] V.M. Laletin, Sov. Technol. Phys. Lett. 17 (1991) 1342.
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M.B. Kothale et al. / Materials Chemistry and Physics 77 (2002) 691–696
[3] M. Maheshkumar, A. Srinivas, S.V. Suryanaryana, G.S. Kumar, T. Bhimankara, Bull. Mater. Sci. 21 (1998) 251. [4] S.V. Suryanaryana, Bull. Mater. Sci. 17 (1994) 1259. [5] K.K. Patankar, V.L. Mathe, A.N. Patil, S.D. Lotke, Y.D. Kolekar, P.B. Joshi, J. Electroceram. 6 (2) (2001) 115. [6] V.M. Laletin, Sov. Technol. Phys. 18 (1992) 484. [7] A.E. Gelyasin, V.M. Laletin, L.I. Trofimovich, Sov. Technol. Phys. 33 (1988) 1361. [8] L. Srideshmukh, K. Krishna Kumar, S. Bal Laxman, A. Rama Krishna, G. SaSathaiah, Bull. Mater. Sci. 21 (1998) 219.
[9] K.K. Patankar, S.A. Patil, K.V. Sivakumar, Y.D. Kolekar, M.B. Kothale, Mater. Chem. Phys. 65 (2000) 97. [10] S. Upadhyay, Devendrakumar, Omprakash, Bull. Mater. Sci. 19 (1996) 513. [11] J. Kuwata, K. Uchino, S. Nomura, Jpn. J. Appl. Phys. 21 (1982) 1298. [12] H.D. Megaw, Ferroelectricity in Crystals, Academic Press, New York (1957). [13] Omparkash, K.D. Mandal, C.C. Christopher, M.S. Sastry, Devendrakumar, Bull. Mater. Sci. 17 (1994) 253. [14] D. Adler, J. Feinleib, Phys. Rev. B 2 (1970) 3112.
Dielectric behaviour and magnetoelectric effect in copper–cobalt ferrite + barium lead titanate composites M.B. Kothale a , K.K. Patankar b , S.L. Kadam b , V.L. Mathe b , A.V. Rao b , B.K. Chougule b,∗ b
a KLE Society’s GIB College, Nipani 591237, Karnataka, India Composite Materials Laboratory, Department of Physics, Shivaji University, Kolhapur 416004, Maharashtra, India
Received 21 November 2001; received in revised form 2 January 2002; accepted 16 February 2002
Abstract ME composites of Cu0.6 Co0.4 Fe2 O4 +Ba0.8 Pb0.2 TiO3 were prepared using a conventional ceramic double sintering process. The presence of phases was confirmed by X-ray diffraction (XRD). The variation of dielectric constant (ε ) in the frequency range 100 Hz–1 MHz and also with temperature at constant frequency was studied. The conduction phenomenon is explained on the basis of small polaron hopping model. The confirmation of this phenomenon is made with the help of AC conductivity measurements. The static value of magnetoelectric conversion factor that is dc(ME)H was studied as a function of intensity of the magnetic field. The maximum value of ME coefficient was observed for 15% ferrite + 85% ferroelectric phase. © 2002 Elsevier Science B.V. All rights reserved. Keywords: ME composites; Polaron hopping; Dielectric behaviour; Magnetoelectric effect
1. Introduction Ferrite-ferroelectric composites consist of two phases viz. piezomagnetic and piezoelectric. The magnetoelectric effect is a coupled, two field effect in which the application of electric field induces magnetization and magnetic field induces electric polarization [1]. It is due to the strain induced in the piezomagnetic/ferrite phase by the applied magnetic field, being mechanically coupled to stress induced in the piezoelectric/ferroelectric phase, the coupling resulting in an electric voltage [2,3]. The ME composites have been exploited as sensors, waveguides, switches, phase invertors, modulators, etc. [4]. ME composites also find a lot of technological applications in radioelectronics, optoelectronics, microwave electronics and transducers in instrumentation. The selection of suitable combination of piezoelectric and piezomagnetic material with a view to achieve ME effect itself is however a challenging task. In order to achieve better ME effect, the piezomagnetic coefficient of ferrite phase and the piezoelectric coefficient of ferroelectric phase must be high. The resistivity of both the phases is comparable and the mechanical coupling between the two phases is perfect [5]. The work reported in the literature is confined to measurement of ME effect in the composites containing a ferroelectric as the first ∗ Corresponding author. Tel.: +91-0231-690571; fax: +91-0231-691533.
component and Ni, Co, Mn ferrites [6,7] as the second component. In the present case copper–cobalt ferrite has been chosen with a view to introduce large Jahn–Teller distortion in the ferrite lattice which will in turn induce more mechanical coupling between the ferroelectric and ferrite phases and may yield maximum ME signal. Hence we report here our results on the measurements of dielectric constant (ε ), loss tangent (tan δ), AC conductivity and ME effect in case of Cu0.6 Co0.4 Fe2 O4 –Ba0.8 Pb0.2 TiO3 composites. These measurements throw some light on the conduction mechanism and ME conversion factor.
2. Preparation of ME composites The ME composites were prepared by normal solid state reaction. The ferrite phase viz. Cu0.6 Co0.4 Fe2 O4 was prepared through solid state reaction using CuO, CoCO3 and Fe2 O3 powders in stoichiometric proportions. The ferroelectric phase viz. Ba0.8 Pb0.2 TiO3 was prepared with BaO, PbO and TiO2 as starting materials. The ferrite powder was presintered at 700 ◦ C for 12 h and ferroelectric at 800 ◦ C for 4 h. After presintering, the constituent phases were thoroughly mixed and ground to fine powder. The ME composites were prepared by mixing 15, 30 and 45% of ferrite phase with 85, 70 and 55% ferroelectric phase respectively. They were presintered at 900 ◦ C for 12 h. The pellets of
0254-0584/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 4 - 0 5 8 4 ( 0 2 ) 0 0 1 3 5 - 9
692
M.B. Kothale et al. / Materials Chemistry and Physics 77 (2002) 691–696
the composite were finally sintered at 1050 ◦ C for 24 h and furnace cooled.
3. Experimental details The composites were characterized by using X-ray diffractometer (Phillips Model PW 1710) using Cu K␣ radiation. The X-ray diffraction (XRD) pattern of the composite phase containing 30% Cu0.6 Co0.4 Fe2 O4 + 70% Ba0.8 Pb0.2 TiO3 is shown in Fig. 1. From the figure it is revealed that both the ferrite as well as ferroelectric phases are present. No irregular peaks have been found in the pattern which confirms single phase formation of composites. Lattice parameters for both the phases have been calculated. Ferrite phase has a cubic spinel structure and ferroelectric phase has a tetragonal perovskite structure. The lattice parameter for ferrite phase in the 30% ferrite composite is 8.28 Å. The lattice parameters for ferroelectric phase in 70% ferroelectric composite are a = 3.877 and c = 3.964 Å and c/a ratio equal to 1.022. The palletized samples were coated with silver paste to ensure good electric contacts. Dielectric measurements were carried out using LCR meter (Model HP 4284A) in conjunction with laboratory designed cell. The dielectric constant
was calculated by using the formula ε =
Cd ε0 A
(1)
where C is the capacitance of pellet in farad, d the thickness of the pellet and A the area of the pellet. The variation of dielectric constant for different frequencies as well as at different temperatures was studied along with the variation of AC conductivity with frequency. To obtain ME signal the palletized samples were poled electrically. For electric poling the samples were heated above their ferroelectric transition temperature in applied high electric field (2 kV cm−1 ) and then allowed to cool slowly in the field. Magnetic poling was carried out by keeping the dc magnetic field for 30 min in the saturation field of 1.5 kOe at room temperature. The electric field (E) developed at different dc field (H) was measured. From the measurements dE/dH for different values of H were calculated.
4. Results and discussion The variation of dielectric constant (ε ) with frequency for the composite xBa0.8 Pb0.2 TiO3 –(1 − x)Cu0.6 Co0.4 Fe2 O4 is shown in Fig. 2. An examination of the figure reveals the
Fig. 1. XRD pattern of 30% Cu0.6 Co0.4 Fe2 O4 –70% Ba0.8 Pb0.2 TiO3 composite.
M.B. Kothale et al. / Materials Chemistry and Physics 77 (2002) 691–696
693
Fig. 2. Variation of dielectric constant with frequency for the composite system: xBa0.8 Pb0.2 TiO3 –(1 − x)Cu0.6 Co0.4 Fe2 O4 .
dielectric dispersion. The ε rapidly decreases at lower frequencies and remains fairly constant at higher frequencies. The large values of dielectric constant at low frequencies is due to dislocations and other defects [8,9]. In case of ferrites and ferroelectric materials this large value of ε has been attributed to the effect of heterogeneity of the samples like pores and layered structure. However, in case of composites it is ascribed to the fact that ferroelectric regions are surrounded by non-ferroelectric regions similar
to the relaxor ferroelectric materials [10]. This gives rise to interfacial polarization which is reflected by sharp fall in ε . Polaron hopping mechanism resulting in electronic polarization also contributes to low frequency dispersion. The static value of dielectric constant in the present samples lies in the range 200–800 and is almost frequency independent. It is further observed that the value of ε increases with increase in ferroelectric content. The variation of tan δ with frequency shows similar behaviour.
Fig. 3. Variation of dielectric constant with temperature for the composite: 70% Ba0.8 Pb0.2 TiO3 –30% Cu0.6 Co0.4 Fe2 O4 .
694
M.B. Kothale et al. / Materials Chemistry and Physics 77 (2002) 691–696
Table 1 Electrical data of xBa0.8 Pb0.2 TiO3 –(1 − x)Cu0.6 Co0.4 Fe2 O4 composites Composition
ε RT
εmax
Tc (K)
γ
α RT (V K−1 )
x x x x
677 1900 1720 1000
1250 2700 3700 2480
455 425 420 415
1.21 1.51 1.63 1.41
400 720 820 960
=1 = 0.85 = 0.7 = 0.55
The variation of dielectric constant (ε ) with temperature is shown in Fig. 3. From the figure it is revealed that ε increases with temperature upto Curie temperature (Tc ) and then it decreases. It is observed from the figure that region around dielectric peak was broadened at all frequencies. The broadening of the peak may be due to microscopic heterogeneity in the composites [5]. The transition is diffused type. In the paraelectric region ε in these composites obeys the relation [10] 1 (T − Tc )2 1 = + ε max 2γ ε max ε
(2)
where γ is the diffusivity parameter, a measure of broadness of the peak in diffused phase type behaviour (DPT). The value of γ for the present system lies between 1 and 2. This parameter varies between 1 for normal Curie–Weiss type and 2 for typical DPT type [11]. The values of ε , Curie temperature, diffusivity parameter and Seebeck coefficient are reported in Table 1 for all the composites. From Table 1 it can be seen that the Curie temperature decreases as the ferroelectric content decreases. This may be due to the statistical fluctuations in compositions in these microregions. Further, the thermoelectric power (α) increases with decrease in ferroelectric content, which may be due to the localized electronic state for the oxides [12]. The variation
of tan δ with temperature at 1 kHz is shown in Fig. 4. This behaviour is similar to the behaviour of ε versus temperature. Here also the peaks become broad near Curie temperature which indicates DPT type behaviour. In order to understand mechanism of conduction AC conductivity was measured as a function of frequency in the range 100 Hz–1 MHz at room temperature. AC conductivity obeys the following relation: σAC = Aω
(3)
where ω is the angular frequency. Fig. 5 indicates that AC conductivity (σ AC ) increases with increase in frequency. Similar results were obtained by other workers [9,13,14]. Frequency dependence of AC conductivity indicates that conduction occurs by hopping of charge carriers among localized states. The conduction is due to small polarons. The variation of magnetoelectric output (dE/dH) versus magnetic field (H) is shown in Fig. 6. For the present system ME output is found to be maximum for 85% ferroelectric + 15% ferrite composite. The dE/dH remains constant for lower magnetic field but at higher magnetic fields it decreases. The constant value of magnetoelectric conversion factor indicates magnetostriction reached its saturation value at the time of magnetic poling. In the present system appearance of ME signal is due to the strain induced by lattice distortion in the ferrite phase by Jahn–Teller ions like Cu. Hence Jahn–Teller effect in the ferrite can lead to polarization in the piezoelectric phase. After a certain field (1.9 kOe), the magnetostriction and strain produced would produce a constant electric field in the piezoelectric phase. Due to this constant field E there is decrease in dE/dH at higher magnetic fields. Further it is observed that the similar trend of variation is observed for all the three composites. As the ferrite content increases the ME output decreases.
Fig. 4. Variation of loss tangent with temperature for the composite: 70% Ba0.8 Pb0.2 TiO3 –30% Cu0.6 Co0.4 Fe2 O4 .
M.B. Kothale et al. / Materials Chemistry and Physics 77 (2002) 691–696
695
Fig. 5. Variation of AC conductivity with angular frequency for the composite system: xBa0.8 Pb0.2 TiO3 –(1 − x)Cu0.6 Co0.4 Fe2 O4 .
Fig. 6. Variation of static magnetoelectric conversion factor with magnetic field for the composite system: xBa0.8 Pb0.2 TiO3 –(1 − x)Cu0.6 Co0.4 Fe2 O4 .
5. Conclusions The XRD patterns of these composites reveals the presence of both ferrite and ferroelectric phases. The number of peaks corresponding to ferrite phase increases with increase in mol% of ferrite. The dielectric behaviour suggests the dielectric dispersion at lower frequencies. This is due to the interfacial polarization and also due to the heterogeneity of the samples. The variation of dielectric constant with temperature gives the broad maximum near the Curie temperature. This suggests DPT type behaviour similar to relaxor ferroelectrics. The variation of AC conductivity with frequency is linear in nature suggesting that the conduction is due to polaron hopping. The magnetoelectric conversion factor (dE/dH) for all the three composites is due to the strain
induced by the lattice distortion in ferrite and also magnetostriction produced due to the applied magnetic field.
Acknowledgements Authors are very thankful to late Prof. S.A. Patil, Ex-Head, Department of Physics for his constant encouragement and help throughout this work.
References [1] C.-W. Nan, Phys. Rev. B 50 (1994) 6082. [2] V.M. Laletin, Sov. Technol. Phys. Lett. 17 (1991) 1342.
696
M.B. Kothale et al. / Materials Chemistry and Physics 77 (2002) 691–696
[3] M. Maheshkumar, A. Srinivas, S.V. Suryanaryana, G.S. Kumar, T. Bhimankara, Bull. Mater. Sci. 21 (1998) 251. [4] S.V. Suryanaryana, Bull. Mater. Sci. 17 (1994) 1259. [5] K.K. Patankar, V.L. Mathe, A.N. Patil, S.D. Lotke, Y.D. Kolekar, P.B. Joshi, J. Electroceram. 6 (2) (2001) 115. [6] V.M. Laletin, Sov. Technol. Phys. 18 (1992) 484. [7] A.E. Gelyasin, V.M. Laletin, L.I. Trofimovich, Sov. Technol. Phys. 33 (1988) 1361. [8] L. Srideshmukh, K. Krishna Kumar, S. Bal Laxman, A. Rama Krishna, G. SaSathaiah, Bull. Mater. Sci. 21 (1998) 219.
[9] K.K. Patankar, S.A. Patil, K.V. Sivakumar, Y.D. Kolekar, M.B. Kothale, Mater. Chem. Phys. 65 (2000) 97. [10] S. Upadhyay, Devendrakumar, Omprakash, Bull. Mater. Sci. 19 (1996) 513. [11] J. Kuwata, K. Uchino, S. Nomura, Jpn. J. Appl. Phys. 21 (1982) 1298. [12] H.D. Megaw, Ferroelectricity in Crystals, Academic Press, New York (1957). [13] Omparkash, K.D. Mandal, C.C. Christopher, M.S. Sastry, Devendrakumar, Bull. Mater. Sci. 17 (1994) 253. [14] D. Adler, J. Feinleib, Phys. Rev. B 2 (1970) 3112.