Abstract: Low density polyethylene (LDPE) nanocomposites
with 3, 5 and 7 wt. % cobalt ferrite (CoFe2O4) nanopowder fabricated
with extrusion mixing and followed up by hot press to reach compact
samples. The transmission/reflection measurements were carried out
with a network analyzer in the frequency range of 8-12 GHz. By
increasing the percent of CoFe2O4 nanopowder, reflection loss (S11)
increases, while transferring loss (S21) decreases. Reflectivity (R)
calculations made using S11 and S21. Increase in percent of CoFe2O4
nanopowder up to 7 wt. % in composite leaded to higher reflectivity
amount, and revealed that increasing the percent of CoFe2O4
nanopowder up to 7 wt. % leads to further microwave absorption in
8-12 GHz range.
Abstract: The mechanical deformation and the electrical conductivity of lanthanum strontium cobalt ferrite oxide under uniaxial compression were investigated at various temperatures up to 1073 K. The material reveals a rather complex mechanical behaviour related to its ferroelasticity and completely different stress-strain curves are obtained during the 1st and 2nd loading cycles. A distinctive ferroelastic creep was observed at 293 K whilst typical ferroelastic stress-strain curve were obtained in the temperature range from 473 K to 873 K. At 1073 K, on the other hand, high-temperature creep deformation was observed instead of ferroelastic deformation. The conductivity increases with increasing compressive stress at all the temperatures. The increase in conductivity is related to both geometrical and piezoelectric effects. From 293 K to 873 K, where the material exhibits ferroelastic behaviour, the variation in the total conductivity decreases with increasing temperature. The contribution of the piezoelectric effect to the total conductivity variation also decreases with increasing temperature and the maximum in piezoconductivity has a value of about 0.75 % at 293 K for a compressive stress of 100 MPa. There is no effect of domain switching on conductivity except for the geometric effect. At 1073 K, the conductivity is simply proportional to the compressive strain.