Influence of Ceramic Particle Sizes on Electrical Properties of Lead Zirconate Titanate (PZT)/Nylon57 Composites

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1 Journal of Metals, Materials and Minerals. Vol.1 No , Influence of Ceramic Particle Sizes on Electrical Properties of Lead Zirconate Titanate ()/Nylon57 Composites Wilairat SUPMAK, Atitsa PETCHSUK and Aree THANABOONSOMBUT National Metal and Materials Technology Center, Pathumthani 11, Thailand 11 Thailand Science Park, Paholyothin Road, Klong 1, Klong Luang, Pathumthani 11 Abstract Received Nov. 5, Accepted Feb. 11, 9-3 connectivity of lead zirconate titanate () with various particle sizes and nylon57 composites were prepared using 3% by volume. Electrical properties of the composites as a function of particle sizes were studied. The relative permittivity, polarization and piezoelectric coefficient (d 33 ) of composites increased with increasing of particle sizes. The optimum relative permittivity and polarization of composite was obtained when 95 μm of average particle size was employed. Piezoelectric coefficient d 33 of the composite was found optimum at pc/n whereas the relative permittivity was about 73 and the remanent polarization was 13 µc/cm. Key words : Lead zirconate titanate (), Nylon 57, Composite, Pizoelectric properties Introduction Composite materials have been intensively studied due to their excellent piezoelectric properties. They have been utilized in variety of applications such as sensors, actuators and under water acoustic transducers.(1-) Composite materials combine the exceptional toughness of polymer materials with the excellent ferroelectric properties of ceramics. They possess good ferroelectric properties with mechanical strength, low acoustic impedance of matching to water and human tissues and ease of processing. (5-) The simplest type of piezo ceramic/ polymer composite is a -3 connectivity, which consists of a polymer matrix filled with piezoceramic particles. (9-11) For -3 connectivity composite, it is not easy to obtain good piezoelectric properties due to the difficulty in poling ceramic particles in such composite. (1-13) One factor that affects the efficiency of poling ceramic particles is the ceramic particle size. Therefore, this work aimed at studying the influence of ceramic particle size on the electrical properties of ceramic/polymer composite. Various ceramic particle size ranges such as after ball mill h, <1 μm, 17- μm, 7-79 μm and >79 μm were composited with nylon 57 in -3 connectivity pattern and their polarization, relative permittivity and piezoelectric coefficient (d 33 ) were investigated. Materials and Experimental Procedures Materials Lead Zirconate Titanate () powder used in the experiment was 5 (APC International Ltd.) which possess the relative permittivity of 175 at, piezoelectric constant d 33 of pc/n and the Curie transition (T c ) of 3 C. powder were consecutively calcined at 5 C and sintered at 11 C for h prior to use. Various particle size ranges of were differentiated by sieving through nylon cloth. The ranges of particle sizes used in this investigation were ball mill h, <1 μm, 17- μm, 7-79 μm and >79 μm corresponding to average particle size of 5 µm, 1 µm, 3 µm, 7 µm, 95 µm, respectively by Mastersizer. Nylon57 was synthesized by melt polycondenzation at 19- C for 5 h according to Cui et al. s method. (1) Preparation of Composite Films All composites were prepared by combined methods of colloidal and melt-press processing techniques. Typically, nylon57 was first dissolved in trifluoroethanol. 3% by volume of selected particle size range of powder was then added into the nylon57 solution while sonicated. The mixture was cast on a petridish to evaporate solvent after sonicated for min. Dried composite film was then hot-pressed for several times until it became homogeneous. The thickness of composite film is approximately -35 μm. Phone -5-5, atitsp@mtec.or.th

2 1 SUPMAK, W. et al. Characterization and Electrical Measurements XRD was used to investigate the crystallinity and crystallographic phase of powder to ensure the tetragonal phase (ferroelectric phase). For electrical measurements, the composites films of 1 cm diameter sample were electroded by gold sputtering on both sides. The composite samples were then poled by corona poling technique at room temperature by applying voltage of kv (.55 ma). The P-E hysteresis loop was measured at room temperature using RTA Standardized Ferroelectric Measurement Test System (radian Technology). The relative permittivity was measured using 19A Impedance Gain/Phase analyzer (Hewlett Packard) at the frequencies from to and the temperature range of -7 C to C. The piezoelectric coefficient d 33 was measured after h of poling by using piezoelectric d 33 meter, model PM31. Results and Discussion The phase formation behavior of powder calcined and sintered at various temperatures was revealed by an X-ray diffraction pattern (XRD) in Figure 1. It was shown that powder calcined and sintered at the temperature range of to 15 C were mainly perovskite structure having tetragonal phase, which indicated by plane (1), () and (11). (15) As the sintering temperature goes higher, the intensities of the () and (1) x-ray reflections get higher meaning that phase are getting close to perfect tetragonal phase. However, when the sintering temperature gets higher than 11 C, the morphology of is changed due to the melting of grain boundaries. Therefore, in this work, powder sintering at 11 C which retained both crystallography and morphology was used for most parts of the study. Figure. Shows cross-sectional SEM images of 3% by volume composites with various particle ranges. The homogeneous distribution of particles in the polymer matrix can be seen from these SEM images. The particles were surrounded by layer of the polymer matrix and there is no large agglomeration of particles. More connection of particles is expected in bigger particle size which may lead to better electrical properties. P-E hysteresis loops of the 3% by volume of /nylon57 composites with various particle sizes measured at room temperature and 5 kv/cm applied electric field were shown in Figures 3a-3e. It can be seen that the particle size has a significant influence on the polarization of composites but less influence on the coercive field. The polarization and coercive field of composites with various ceramic particle sizes were summarized in Table 1. It can be concluded that the larger the particle size, the higher the polarization. The spontaneous polarization (Ps) and remanent polarization (Pr) showed the highest value when the having average particle size of 95 μm was used. Intensity (counts) θ Figure.1 XRD patterns of powders calcined and sintered at various temperatures C 1 C 11 C 1 C 15 C for h at heating/cooling rate of C/min. Figure. Cross-sectional SEM image of 3% by volume of /nylon57 composites with various particle sizes ball mill h (5 µm) < 1 µm (1 µm) 17- µm (3 µm) 7-79 µm (7 µm) > 79 µm (95 µm)

3 Influence of Ceramic Particle Sizes on Electrical Properties of Lead Zirconate Titanate ()/Nylon57 Composites Polarization (uc/cm ) Polarization (uc/cm ) Polarization (uc/cm ) Polarization (uc/cm ) Polarization (uc/cm ) Relativepermitivity Figure 3. The P-E hysteresis loops of 3% by volume of /nylon57 composite with various particle ranges ball mill h (5 µm) < 1 µm (1 µm) 17- µm (3 µm) 7-79 µm (7 µm) > 79 µm (95 µm) Table 1. A summary of polarization of 3% by volume of /nylon 57 composite with various particle size ranges. Particle size range (μm)* ball mill h (5μm) P s (µc/cm ) E = 5 kv/cm, RT P r (µc/cm ) E c (kv/cm) <1 (1 μm) (3 μm) (79 μm) >79 (95 μm) 1 13 *The number in parenthesis is average particle size of ceramic particle by Matersizer Figure. and dielectric loss of 3% by volume of /nylon57 composite with various particle ranges ball mill h (5 µm) < 1 µm (1 µm) 17- µm (3 µm) 7-79 µm (7 µm) > 79 µm (95 µm) The temperature dependence of relative permittivity and dielectric loss of /nylon 57 composites having particle size of ball mill h (5 µm), <1 (1 µm), 17- (3 µm), 7-79 (7 µm) and >79 μm (95 µm) were investigated as a function of frequencies (1, 1, 1 and ) from -7 to 1 C and were shown in Figure a-e. The relative permittivity increased with the increase of temperature. The relaxation located around 5-7 C and centered at 5 C was characterized as β-relaxation which associated with the glass-rubbery transition (T g ) of the polymer. Segmental mobility of the polymer molecules increased with temperature leading to an increase in relative permittivity. Conductivity relaxation appeared for temperatures far above T g and low frequency ranges emphasizing the contribution of the conduction due to the increase in the mobility of electric charges in the polymer

4 15 SUPMAK, W. et al. versus temperature. (1) The highest relative permittivity at room temperature of composite was obtained when having average particle size of 95 μm was employed. As particle size became smaller, the relative permittivity as well as dielectric loss was also lower. The effect of particle sizes on piezoelectric coefficient (d 33 ) of /Nylon57 composite was summarized in Table. With an increase of particle size, the piezoelectric coefficient (d 33 ) was increased. The highest piezoelectric constant d 33 of the composite was obtained at pc/n where having average particle size of 95 μm was used. An increase of the relative permittivity and piezoelectric coefficient d33 with increasing of particles size are probably due to dense connection of particles resulting in higher poling efficiency. Hence, the larger particle size e.g. 95 μm provides better piezoelectric properties. Table also compared electrical properties of composites of the previous work (17) with our present results. From our results, it is clearly seen that the particle size of has an effect on electrical properties of the /Nylon57 composites, thus agreeing with earlier results by A. Chaipanich where the cement composite with larger particle size of μm exhibits better properties than that of smaller size (3. μm). However, our recent work shows that the -3 composite at 3% by volume with average particle sizes of 95 μm exhibits a comparable piezoelectric coefficient d 33 value to that of the earlier works which comprises 5% by volume with particle sizes at μm. This infers that less was used in our composites in order to get comparable piezoelectric constant d 33. In addition, the powders used in this work were sintered at lower sintering temperature (11 C) suggesting low energy and cost effective in preparing composites. Conclusions The particle size of is clearly affected electrical properties of the /nylon57 composite. The remanent polarization, relative permittivity and piezoelectric coefficient (d 33 ) of composites increased with increasing of particle size. The optimum remanent polarization, relative permittivity and piezoelectric coefficient (d 33 ) of composites were obtained with average particle size of 95 μm. An enhancement of the relative permittivity and piezoelectric coefficient (d 33 ) of larger particle size was contributed to dense connection of particle which facilitate the poling process resulting in high poling efficiency and high electrical properties. Acknowledgments This work is financially supported by National Metal and Materials Technology Center under the project No. MT-B--CER-7-1-I References 1. Dong, L., Xiong, C., Quan, H. and Zhao, G.. Polyvinyl-butyral/lead zirconate titanates composites with high dielectric constant and low dielectric loss. Scripta Mater. 55 : Table. Comparing of electrical properties of present composites with those of the previous work. Ref. sintered ( C) % vol. particle size range (μm)* A.Chaipanich (17) 15/3h /3h εr loss d33 (pc/n) 15/3h /h 3 ball mill h (5μm) /h 3 <1 (1 μm) Present work 11/h (3 μm) /h (79 μm) 9. 11/h 3 >79 (95 μm) 73. *The number in parenthesis is average particle size of ceramic particle by Matersizer

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