Effect of piezoelectric grain size on magnetoelectric coefficient of Pb(Zr 0.52 Ti 0.48 )O 3 –Ni 0.8 Zn 0.2 Fe 2 O 4 particulate composites Rashed Adnan Islam Æ Shashank Priya Received: 14 December 2007 / Accepted: 14 February 2008 / Published online: 23 March 2008 Ó Springer Science+Business Media, LLC 2008 Abstract This study investigates the variation of mag- netoelectric (ME) coefficient as a function of the piezoelectric grain size in the composite system of 0.8 Pb(Zr 0.52 Ti 0.48 )O 3 –0.2 Ni 0.8 Zn 0.2 Fe 2 O 4 . It was found that as the piezoelectric-phase grain size increases the overall resistivity, piezoelectric, dielectric, and ferroelectric prop- erty of the composite increases and saturates above 600 nm. Below 200 nm average grain size, piezoelectric and dielectric properties decrease rapidly. The ferroelectric Curie temperature was found to decrease from 377 to 356 °C as the average grain size decreases from 830 to 111 nm. ME coefficient of the composite showed a rapid change below grain size of 200 nm and was found to saturate above 600 nm to a value of 155 mV/cm.Oe. Introduction Magnetoelectric (ME) effect in particulate sintered com- posites has been obtained by combining magnetostrictive and piezoelectric phases [1–5]. Sintered composites con- sisting of piezoelectric phases, Pb(Zr, Ti)O 3 and BaTiO 3 , and ferromagnetic phases, CoFe 2 O 4 , NiFe 2 O 4 , LiFe 5 O 8 , and CuFe 2 O 4 , have been widely studied because of sim- plicity in synthesis using conventional ceramic processing [6–11]. Composition, microstructure, and geometry play important role on the magnitude of the ME coefficient. The effect of composition variation has been investigated by doping the PZT and ferrites, and utilizing relaxor-based compositions. The effect of geometry has also been investigated by synthesizing bilayers, sandwich structures, 2-1 composites, and 2-2 composites. However, the effect of microstructure has not been studied in detail. The pio- neering studies at Phillips Laboratories showed that texturing improves the ME coefficient by providing higher piezoelectric coefficients. In this study, we elucidate the effect of piezoelectric grain size on the magnitude of ME coefficient. We select the model system, 0.8 Pb(Zr 0.52 Ti 0.48 )O 3 –0.2 Ni 0.8 Zn 0.2 Fe 2 O 4 [PZT–20 NZF], for this study. Effect of grain size on piezoelectric, dielectric, and ferroelectric properties has been widely studied in literature [12–16]. It is well known that piezoelectric, and dielectric properties drop rapidly below critical grain size (*100 nm) [17, 18]. SEM analysis combined with the surface tension measurement indicate that the surface bond contraction due to small size induces a compressive stress on the inner part of a grain and this effect plays an important role in ferroelectric materials in the nanometer size range. The induced stress causes decrease of Curie temperature and spontaneous polarization with decreasing grain size. The domain wall contribution has an opposite effect as compared with the surface bond contraction induced effect. When the grain size decreases to a value comparable to the width of domain walls, pinning points develop inside the grains and the domain wall motion is inhibited. The reduced wall mobility causes a decrease in the relative permittivity. The measured value is a compe- tition between the increase of relative permittivity by the surface bond contraction effect and its decrease by the domain wall pinning effect [19–22]. R. A. Islam Materials Science and Engineering, University of Texas at Arlington, Arlington, TX 76019, USA S. Priya (&) Materials Science and Engineering, Virginia Tech, Blacksburg, VA 24061, USA e-mail: spriya@vt.edu 123 J Mater Sci (2008) 43:3560–3568 DOI 10.1007/s10853-008-2562-9