Electrical and magnetic properties of NI-TI substituted perovskites.
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Date
2018
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Abstract
All perovskites samples studied in this work: (La,Bi,Sr)Ni0.25Ti0.25Fe0.5O3 were synthesized
by a combination of high energy ball milling (HEBM) on a Retsch PM 400 instrument
and heat treatment on a Sentro Tech (type: STT-1600C-3-24) high temperature
tube furnace. These samples were selected in anticipation of a future study of gas sensing
properties not undertaken in this work because of equipment constraints. The additional
Ni0:5Ti0:5Fe2O4 spinel ferrite was synthesized by HEBM. The compounds were characterized
by X-ray di raction (XRD), Fourier transform infrared spectroscopy (FTIR), high
resolution transmission electron microscopy (HRTEM), M ossbauer spectroscopy, vibrating
sample magnetometer (VSM) at temperatures between 10 K and 300 K, resistivity
four probe method, Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BHJ)
for surface area measurements.
The X-ray di raction data for LaNi0.25Ti0.25Fe0.5O3 (LNTFO) showed the formation of
single phase compound with orthorhombic structure which is similar to that of reported
LaFeO3. The average particle size obtained from HRTEM was 91 5 nm. The cosubstitution
of Ni2+ and Ti3+ at the Fe3+ site indicated enhanced magnetic properties.
Magnetization measurements showed soft ferromangetic behavior with saturation magnetisation
MS in the range 2.25 0.2 emu/g (at 300 K) to 2.61 0.2 emu/g (at 10 K). The
coercivity increased from 0.36 0.02 kOe to 0.41 0.02 kOe with decreasing temperatures.
M ossbauer data revealed the sample was magnetically ordered at room temperature. The
isomer shift values indicated possible strong covalent bonds between metal and the oxygen
ions and existence of only Fe3+ ions in the structure. Furthermore, the milled material
showed semiconducting behavior with activation energy of 3.4 0.1 eV whilst the milled
and annealed sample has lower activation energy of 0.9 0.06 eV.
A BiNi0.25Ti0.25Fe0.5O3 (BNTFO) perovskite compound has been successfully synthesized
by high energy ball milling and annealing. The crystallites size were obtained to be in
the range 10 nm to 70 nm. The grains were observed to be semi-spherical with good
surface coverage. We found improved saturation magnetization relative to the LNTFO
sample with MS in the range 6.5 0.2 emu/g (at 300 K) to 7. 3 0.2 emu/g (10 K) and
the coercivity in the range 0.49 0.02 kOe (300 K) to 0.62 0.02 kOe (10 K). M ossbauerspectrum reveals magnetic ordering at room temperature. Isomer shift values indicated
only the presence of Fe3+ ions. Magnetic hyper ne values at 300 K were obtained to be
518 5 kOe and 510 4 kOe for the A and B sites respectively. A low activation energy
of 0.66 0.02 eV was obtained for this sample.
SrNi0.25Ti0.25Fe0.5O3 (SNTFO) belonging to an orthorhombic crystal system showed paramagnetic
behavior at room temperature whilst at lower temperatures it was superparamagnetic.
The magnetization MS was relatively low ranging from 14.14 0.23 emu/g to
0.0032 0.0001 emu/g and the coercive eld increased with decreasing temperature from
0.34 0.06 kOe to 1.14 0.06 kOe. The M ossbauer spectrum indicated the presence of
both Fe4+ and Fe3+ iron ions which is consistent to that reported for SrFeO3 compounds.
Particle size obtained from FETEM averaged 127 12 nm and the surface morphology
was indicative of a rough absorber surface with semi-spherical grains of di erent sizes.
An activation energy of 0.37 0.03 eV for the annealed SNTFO indicated good electronic
conductivity at relatively higher temperature.
An additional Ni0.5Ti0.5Fe2O4 compound was successfully synthesized by HEBM. The
sample was characterized by quick phase formation. Prolonged milling destroyed the
phase. From the structural analysis it was evident that starting precursors for a chemical
reaction are of vital importance as they have great in
uence on the reaction product.
The mean particle size was obtained to be 45 9 nm. Particle size reduced with milling
time whilst the strain increased. The coercivity and saturation magnetization appeared to
follow the Stoner{Wohlfarth model in two distinct regions at high temperatures (300 K to
100 K) and low temperatures (50 K to 10 K) with approximately equal anisotropies in each
temperature range. Saturation magnetization was obtained to be between 38.73 0.03
emu/g to 38.84 0.03 emu/g and the coercivity was between 820 32 Oe to 407 32 Oe.
Room temperature M ossbauer spectrum revealed hyper ne elds of 446 1 kOe and 480 1
kOe for A and B sites respectively. Isomer shift values indicated co-existence of both Fe3+
and Fe2+.
Description
Master’s Degree. University of KwaZulu-Natal, Durban.