  Bulk magnetodielectric composites with a 3/0 configuration comprising of
ferroelectric/magnetostrictive phases have been synthesized using
Sr0.5Ba0.5NbO6 / CoCr0.4Fe1.6O4 as the two constituents respectively. The
ferroelectric phase made by a dual stage sintering process has a uniform grain
size of 15 microns while the magnetostrictive phase has a grain size of 2 to 3
microns. Composites synthesized by conventional solid state processing using
these two constituents exhibits large magnetodielectric coupling at room
temperature which increases with increasing magnetic field. The composite with
30 percent magnetostrictive phase distributed uniformly in the ferroelectric
phase has the most desirable microstructure and exhibits a large coupling with
3.2 percent change in the dielectric constant at 1000 Hz and 8000 Oe magnetic
field. This change in dielectric constant decreases when the fraction of
magnetostrictive phase is varied, indicating that 30 percent is the optimal
value to realize large coupling between the two phases. This result confirms
that 3D percolation causes the coupling to decrease in composites.
