St., Sosnowiec, , Poland b Institute of Physics, University of Silesia, 4, Uniwersytecka St.,

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1 This article was downloaded by: [Dr P. Wawrzała] On: 21 September 2013, At: 00:16 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Ferroelectrics Publication details, including instructions for authors and subscription information: Multiferroic Ceramic Composites Based on PZT Type Ceramic and NiZnFe Ferrite D. Bochenek a, P. Niemiec a, P. Wawrzała a & A. Chrobak b a Department of Materials Science, University of Silesia, 2, Śnieżna St., Sosnowiec, , Poland b Institute of Physics, University of Silesia, 4, Uniwersytecka St., Katowice, , Poland Published online: 20 Sep To cite this article: D. Bochenek, P. Niemiec, P. Wawrzała & A. Chrobak (2013) Multiferroic Ceramic Composites Based on PZT Type Ceramic and NiZnFe Ferrite, Ferroelectrics, 448:1, , DOI: / To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content ) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at

2 Ferroelectrics, 448:96 105, 2013 Copyright Taylor & Francis Group, LLC ISSN: print / online DOI: / Multiferroic Ceramic Composites Based on PZT Type Ceramic and NiZnFe Ferrite D. BOCHENEK, 1 P. NIEMIEC, 1 P. WAWRZAŁA, 1, AND A. CHROBAK 2 1 Department of Materials Science, University of Silesia, 2, Śnieżna St., Sosnowiec , Poland 2 Institute of Physics, University of Silesia, 4, Uniwersytecka St., Katowice , Poland I. Introduction Multiferroic (ferroelectric ferromagnetic) ceramic composites were obtained on the basis of a ceramic powder of PZT type, i.e. Pb(Zr 0.51 Ti 0.49 )O % at. Bi 2 O % at. Nb 2 O % at. MnO 2 (marked as PZTBNM) and Pb 0.84 Ba 0.16 (Zr 0.54 Ti 0.46 )O % at. Nb 2 O 5 (marked as PBZTN). Admixtured compositions constituted of a PZT type ferroelectric powder with nickel-zinc ferrite (Ni 1-x Zn x Fe 2 O 4 ) as the magnetic content in the composite. Synthesis of the composite content was performed using compact sintering in the solid phase, while densification of the synthesized powder was achieved using the pressure-less sintering method (conventional sintering method). For the obtained multiferroic ceramic composites XRD investigations were performed, as well as investigations of microstructure, EDS, dielectric and magnetic properties, impedance and electrical hysteresis loop. The tests showed the existence of a correlation between magnetic and electric subsystems in the composites. Thanks to the ferroelectric and magnetic properties of the composites obtained, materials of this type could be applied, for example, in new memory types or magnetoelectric transducers. Key words Ferroelectromagnetics; multiferroic ceramic composites; PZT type ceramic; nickel-zinc ferrites PZT type ceramics very often constitute the basis for composing solid solutions, allowing improvement of their application parameters because of their unique ferroelectric, electromechanical, pyroelectric and piezoelectric properties [1, 2]. PZT belongs to the family of multi-component solid solutions of (1-x)PbZrO 3 - xpbtio 3 (0 < x < 1) type, where Ti 4+ ions in PbTiO 3 are partly replaced by Zr 4+ ions in the molar ratio x. PZT is of perovskite type structure (ABO 3 ), where Ti 4+ and Zr 4+ cations take B locations in a random pattern, and Pb 2+ cations take A locations [3, 4]. Modifying PZT is the simplest and most efficient way to control the physical properties of PZT ceramics for modern electronics needs (smart materials) [5]. The Pb(Zr 1-x Ti x )O 3 modified solid solution is one of the few materials on the basis of which it is possible to compose many appliances with completely different functions and parameters [1, 2, 6]. Ferrites are chemical compositions of iron oxide Fe 2 O 3 Received September 26, 2012; in final form April 16, Corresponding author. pawel.wawrzala@us.edu.pl [366]/96

3 Composites Based on PZT and NiZnFe Ferrite [367]/97 with other metal oxides. Spinel ferrites are of spinel mineral MgAl 2 O 4 structure (with general formula MeAl 2 O 4, where Me = Fe, Ni, Cd, Zn, Cu, Co, or Mg). Magnetic and electric properties of the spinel ferrites depend on chemical composition and on the cations locations in the tetrahedral and octahedral positions, and the cations distribution depends on the methods of the whole synthesis process. Regarding magnetic properties, ferrites may be divided into soft magnets and hard magnets [7]. They are used in radio-technology, high frequency and ultrasound technologies, and also as coil cores, glands, transformers, or magnetic antennas, etc. [8]. The purpose of this work was to obtain multiferroic ceramic composites on the basis of ferroelectric powder and ferrite. The magnetic ingredient was a nickel zinc ferrite (Ni 0.64 Zn 0.36 Fe 2 O 4 ) and the ferroelectric ingredients were two solid solutions of PZT type with structure belonging to the morphotropic area. Primary properties of the multiferroic ceramic composites were examined. II. Experimental In the multiferroic PZT-ferrite composites the synthesized ferroelectric powder constituted 90%, whereas the ferromagnetic powder was 10%. To obtain the composites, the powders were multi-component solid solutions of PZT type, with ferroelectric properties and the following chemical compositions: Pb(Zr 0.51 Ti 0.49 )O % at. Bi 2 O % at. Nb 2 O % at. MnO 2 (PZTBNM) and Pb 0.84 Ba 0.16 (Zr 0.54 Ti 0.46 )O % at. Nb 2 O 5 (PBZTN). The PZT type components were prepared by solid reaction synthesis. The raw materials were first milled, pressed to pellets then pre-sintered at 850 C for 2 h. The magnetic ingredient was a zinc nickel ferrite powder Ni 0.64 Zn 0.36 Fe 2 O 4 obtained from milled raw powders, and calcined at 900 C for 4 h. Components were ground into a power, milled, and pre-synthesis mixed powders were calcined again at 1050 C for 2 h. The calcined powders were milled again, pressed into 10 mm diameter pellets and sintered at 1250 Cfor 2 h using the pressure-less sintering method. Two multiferroic composites were obtained, marked as follows: PZTBNM ferrite and PBZTN ferrite. Electrodes were applied on the composite specimen surfaces by silver paste burning method for electrical tests. The X-ray measurements were carried out at room temperature on a Phillips diffractometer (with a Cu Kα source and a graphite monochromator, step 0.02 and measurement time 4s/step). The microstructure of fractures test samples were examined on a Hitachi S-4700 SEM field emission scanning microscope with a Noran Vantage EDS system. Impedance and dielectric properties tests were performed on a QuadTech1920 LCR meter, and magnetic properties measurements were using a SQUID magnetometer (MPMS XL-7 Quantum Design) in the range of temperatures from 271 Cto27 C and magnetic field to 7T, and a magnetic Faraday scale in the range of temperatures from 27 C to 827 C. Hysteresis (P-E) loops at various electric field frequencies at room temperature were investigated with a Sawyer-Tower circuit and Matsusada Inc. HEOPS-5B6 precision high voltage amplifier. Data were stored on a PC computer disc using an A/D, D/A transducer card. III. Results and Discussion The X-ray investigations of the PBZTN ceramics (Fig. 1) confirmed that the materials belonged to a group of materials with the perovskite type structure, and belong to the morphotropic area (coexistence of tetragonal and rhombohedral phases), closer to the rhombohedral phase. X-ray examinations of PZTBNM ceramics have shown that at room

4 98/[368] D. Bochenek et al. Figure 1. XRD patterns of the ferrite and PZT-type powders and the composites PZTBNM ferrite and PBZTN ferrite powders. temperature it has a structure of the perovskite type, within the morphotropic area too, but closer the tetragonal phase. The admixtures introduced to PZT type solid solutions move and widen the morphotropic area the coexistence of both phases. X-ray diffraction patterns for the ferrite powder NiZnFe shows a typical single cubic spinel phase. For PZTBNM ferrite and PBZTN ferrite composites, the X-ray analysis showed the existence of strong maxima coming from PZT material phases and also existence of peaks coming from the ferrite NiZnFe - magnetic phase. At the same time, the characteristic maxima (maxima fission) describing the subsequent phases undergo substantial diffusion. The X- ray analysis also confirmed a lack of impurity phases existing in the composite samples obtained. Comparing the two PZT type ceramic samples (PZTBNM and PBZTN), with composites containing ferrite (PZTBNM ferrite and PBZTN ferrite), the pure ceramic samples have a much higher density (Table 1). The EDS (Energy Dispersive Spectrometry) qualitative and quantitative analyses of the element distribution confirmed the presence of elements from both ferrite and ceramic powders of PZT type, and their assumed percentage compositions (Fig. 2a). Fig. 2b c shows microstructural SEM images for fractures in the composite samples of PZT ferrite type. The microstructure of the PZTBNM ferrite is characterized by fine, well crystallized grains of ferroelectric component with high homogeneity Fig. 2b. Ferrite grains are smaller and surrounded by larger grains of PZT powder. In case of composite fracture analysis of PBZTN ferrite, no well developed grains with boundaries were observed, which may indicate too high a sintering temperature (Fig. 2c). Tests for dielectric properties of multiferroic ceramic composites have shown existence of maxima coming from the ferroelectric paraelectric phase transition (Fig. 3). In the ferroelectric phase, the ferroelectric is divided into domains (areas with different polarization directions). The factor that causes its division into domains is energy, which is connected with homogeneous charge distribution on its surface called the depolarization energy. This division is opposed by domain walls (transition layers) causing an energy increase. As a result, balance is reached which corresponds with a minimum of system energy

5 Composites Based on PZT and NiZnFe Ferrite [369]/99 Table 1 Parameters for the PZT ferrite composites PZTBNM PBZTN Parameter ceramics PZTBNM ferrite ceramics PBZTN ferrite ρ [g/cm 3 ] ρ DC 10 5 at T r [ m] T m [ C] (1 khz) ε r (1 khz) ε m (1 khz) tanδ at T r (1 khz) tanδ at T m (1 khz) P R [μc/cm 2 ] E C [kv/mm] M S [Am 2 kg 1 ] Figure 2. a) EDS analysis of elements distribution for NiZnFe ferrite, PZTBNM ferrite and PBZTN ferrite composites, b) SEM microstructure PZTBNM ferrite composite, c) SEM microstructure PBZTN ferrite composite.

6 100/[370] D. Bochenek et al. Figure 3. Temperature dependencies of electric permittivity ε for the composite: a) PZTBNM ferrite and b) PBZTN ferrite (heating). (macroscopic polarization is equal to zero). The change of this macroscopic polarization value rests on the increase of domain volume in one polarization direction, at the cost of the oppositely oriented domains. In ferroelectrics above the transition phase temperature T m, ordering of the long range dipole moments is destroyed by heat movement, and the spontaneous polarization diminishes (permanent dipole moment disappears spontaneous polarization P S ). The phase transition is accompanied by a change of the ferroelectrics symmetry. The dielectric subsystem phase transition in PZTBNM and PBZTN occurs in a narrow temperature range (the dotted line in Fig. 3a, b for frequency 1 khz). Higher values of dielectric permittivity ε m (1 khz) were seen in PBZTN ceramics in comparison with PBZTN ferrite composite. The magnetic ingredient (NiZnFe) in PFN ferrite composite results in ε m decrease, and significant phase transition diffusion. The composites obtained on the basis of PZT type ceramic powder and ferrite powder NiZnFe are characterized with diffused phase transition during transition from ferroelectric into paraelectric state. The extent of diffusion for PZTBNM ferrite and PBZTN ferrite is different. A lot of factors depending on processing decide the level of phase transition diffusion, such as content fluctuations in composite micro-volume, or heterogeneity of defects distribution and mechanical strains, among others. They cause differences in transition temperatures from ferroelectric to paraelectric state in crystallites with different mechanical strain levels, and in crystallites with different content (in the process of ceramics cooling, during transition from ferroelectric to paraelectric state, mechanical strains are also formed in the volume of one crystallite). The domain structure, while being formed, also introduces its strains in the crystallite, and by mutual reaction with other crystallites it influences the phase transition diffusion. So, the phase transition diffusion is the stronger the bigger defects there are in the ceramics structure. The phase transition diffusion of the dielectric subsystem in PZT ferrite type, visible in ε(t) graphs, testifies also to the influence of magnetic properties on their dielectric subsystem. For lower frequencies of the measurement field, the level of phase transition diffusion increases. In the case of PZTBNM ferrite, the decrease in ε m (1 khz) compared to its equivalent in PZT ceramics, is substantially lower, than in the case of the PBZTN ferrite composite and its ceramic equivalent PBZTN, where the decrease in ε m values is as high as 4 - fold.

7 Composites Based on PZT and NiZnFe Ferrite [371]/101 Figure 4. Temperature dependencies for tangent of dielectric losses tanδ for the composite: a) PZTBNM ferrite, b) PBZTN ferrite (heating). The composites of PZT ferrite type obtained on the basis of ceramic powder also have higher values of dielectric losses compared to their ceramic equivalents (dotted line in Fig. 4a, b for v = 1 khz). The multiferroic ceramic composite obtained using PBZTN ceramic powder has lower dielectric losses. Figure 5 shows the electric hysteresis loops for v = 1 Hz, for PZT type ceramics and for multiferroic ceramic composites. P(E) loops show a non-linear dependency of polarization P on external polarization field E. PBZTN material is among the group of Figure 5. Hysteresis loops P (E) for the PZTBNM and PBZTN ceramics as well as PZTBNM ferrite and PBZTN ferrite composites (at room temperature).

8 102/[372] D. Bochenek et al. soft ferroelectric materials, whereas PZTBNM ceramics exhibits properties of medium ferroelectric hardness. Hysteresis loops obtained on the basis of both PZT ceramic composite types show smaller values of remnant polarization and coercivity compared to their ceramic equivalents (Table 1). Magnetic addition in the composites cause the electric hysteresis loops in PZTBNM ferrite and PBZTN ferrite to take a shape characteristic for a linear dielectric with losses. Dependencies of magnetization on temperature M(T) in the external magnetic field 0.1 T for the obtained multiferroic ceramic composites are very similar (Fig. 6a, b). M(T) curves contain two components, that is: ferro/ferrimagnetic with Curie temperature around 400 C and para/super-paramagnetic clearly visible in temperatures below 173 C. It is a proof that in the samples volume there are (besides the big grains with a ferromagnetic arrangement), smaller, non-interacting grains showing para or super paramagnetic properties. Above 135 C there is sizeable magnetization decrease. Above room temperature, around the ferroelectric paraelectric phase transitions, characteristic anomalies are observed in the M(T) graphs (slight waveform inflections). Such a behavior can show the influence of a dielectric subsystem on multiferroic ceramic composite magnetic properties. Above a temperature of 405 C, ferroelectric ferromagnetic composites are paramagnetic. The PBZTN ferrite composite has higher values of magnetic susceptibility in comparison to the PZTBNM ferrite composite. Magnetic hysteresis loops of the multiferroic ceramic composites obtained are characteristic for soft ferromagnetic materials (Fig. 6a,b inside). PBZTN ferrite composite shows higher values of spontaneous magnetization M S (Table 1). Figure 7a, b shows the variation of the real Z and imaginary Z parts of impedance as a function of frequency at different temperatures, varying from 200 C to 400 Cfor PZTBNM ferrite composite, and Fig. 8a,b for PBZTN ferrite composite, respectively. As shown in Fig. 7a and 8a for the analyzed composites, it is observed that the magnitude of Z decreases with an increase in frequency and temperature. Insets in these Fig. shown the magnification of Z and Z (respectively) at the high frequency range. Also, for both analyzed composites, imaginary Z parts of impedance decrease with increasing frequency and temperature too (Fig. 7b and 8b). The values of Z was found to decrease with increasing Figure 6. Magnetization temperature dependencies M(T) for composites: a) PZTBNM ferrite, b) PBZTN ferrite. Inset graph on the left magnetic hysteresis loops at 27 C; inset graph on the right magnetization temperature dependencies for composites in logarithmic scale.

9 Composites Based on PZT and NiZnFe Ferrite [373]/103 Figure 7. Temperature and frequency dependent real (a) and imaginary (b) impedance spectra of PZTBNM ferrite composite. Inset: high frequency range of which magnifies the peak positions (b). temperature, indicating the increasing loss in the samples (increase in conductivity) [9]. For both composites the connection of all the curves at high frequency indicates the depletion of space charges at those frequencies. The space charge polarization mechanism dominates in heterogeneous structures, where a material is assumed to be composed of different areas (grain and grain boundaries). These phases have different electrical conductivity, and thus accumulation of charges will occur at the phase boundary [10]. This result confirms the presence of temperature dependent electrical relaxation phenomena in the composite PZT-ferrite type. This variation of τ can be described by the well known Arrhenius equation (1): ( ) Eτ τ = τ 0 exp (1) k B T where: E τ - activation energy of the relaxation process, k B - Boltzmann constant and τ 0 - characteristic relaxation time at infinite temperature. The plot of lnτ v. 1000/T for the composite PZT-ferrite type is shown in the inset of Fig. 9. The values of E τ and τ 0 were calculated from the intercept and slope of the linear fit and found to be for PZTBNM ferrite composite ev and s, respectively and for PBZTN ferrite composite ev and s, respectively. Figure 8. Temperature and frequency dependent real (a) and imaginary (b) impedance spectra of PBZTN ferrite composite. Inset: high frequency range of which magnifies the peak positions (b).

10 104/[374] D. Bochenek et al. Figure 9. Temperature dependence of the relaxation time τ for PZTBNM ferrite composite (a) and PBZTN ferrite composite (b). Inset: lnτ v.1000/t. IV. Summary Composites obtained on the basis of PZT type ferroelectric powder and NiZnFe ferrite powder are characterized with a diffused phase transition during transition from the ferroelectric to paraelectric state. The extent of phase transition diffusion in PZTBNM ferrite and PBZTN ferrite is different. The multiferroic (ferroelectric ferromagnetic) ceramic composite PZTBNM ferrite is characterized with higher values of maximum permittivity and lower level of phase transition diffusion comparing to PBZTN ferrite composite. However, it has lower values of magnetic susceptibility and spontaneous magnetization. Nevertheless the multiferroic ceramic composite PBZTN ferrite exhibits higher level of phase transition diffusion and higher values of remnant polarization P R. It is also characterized with a high decrease of maximum electric permittivity ε m comparing to PBZTN ceramics. Electric hysteresis loops of the composites take shapes characteristic for dielectrics with losses. However, magnetic hysteresis loops of the obtained composites show behavior characteristic for soft magnetic. Tests of dielectric and magnetic properties of the multiferroic ceramic composites confirm magnetic and electric subsystems. It means that in these types of composites there is possibility of controlling the electric properties through outer magnetic field, and on the contrary controlling magnetic properties by electric field. In future these properties may be used in new types of memory, for example they can make creating four logic states possible (P + M + ), (P + M ), (P M + ), (P M ). References 1. Y. Xu, Ferroelectric materials and their applications. North-Holland, Amsterdam; W. Long, W. Ching-Chuang, W. Tien-Shon, and L. Hsi-Chuan, Improved ceramics for piezoelectric devices. J Phys C: Solid State Phys. 16, 14, (1983). 3. R. Zachariasz and D. Bochenek, Properties of the PZT type ceramics admixed with barium and niobium. Arch Metal Mat. 54, (2009). 4. R. Zachariasz, D. Bochenek, K. Dziadosz, J. Dudek and J. Ilczuk, Influence of the Nb and Ba dopands on the properties of the PZT type ceramics. Arch Metal Mat. 56, (2011). 5. Z. Surowiak and D. Bochenek, Modyfikowanie składu chemicznego elektroceramiki PZT. Materiały ceramiczne/ceramic Materials/. 4, (2004).

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