Crystal structure of sintered pellets
5.5 Microstructure and Relative density
To understand the effects of Co doping on the evolution of microstructure of MTO ceramics, surface morphology of the sintered MTO ceramics were analyzed using SEM as depicted in Figure 5.4. For x = 0.05 sintered at 1100°C, the microstructure displays a small grain structure with finite pores. However, with increasing sintering temperature up to 1200oC, the average grain size increases with an enhancement in compactness along with the uniform microstructure. The average grain sizes were found to be 3.1, 4.0 and 7.4 µm for the samples sintered at 1100oC, 1150oC and 1200oC, respectively. Figures 5.5 (a - d) displays the SEM images of samples doped with different Co content and sintered at 1200oC for 3 h. All the samples are showing dense and pores free uniform microstructures. The average size of the grains increases with increasing Co doping up to x = 0.05, which indicates that Co doping up to x = 0.05 in MTO ceramic promotes the grain growth. The maximum grain size in the
range of 5.5 - 7.4 µm is achieved for the sample with x = 0.05. To study the chemical composition of the prepared samples, EDS spectra were obtained. A typical EDS spectrum for x = 0.05 sample is shown in Figure 5.6 and the chemical composition is found to be (Mg:
Co: Ti: O = 18.58: 1.03: 19.81: 60.59%) (Mg0.95Co0.05)TiO3.
Figure 5.4: SEM images of (Mg0.95Co0.05)TiO3 ceramics sintered at different sintering temperatures: (a) 1100oC, (b) 1150oC, (c) 1200oC, and (d) 1250oC.
Figure 5.5: SEM micrographs of (Mg1-xCox)TiO3 doped with different x concentrations:
o
Figure 5.6: EDS spectrum for x = 0.05 sample sintered at 1200°C for 3 h.
To study the improvement in density of MTO ceramics with Co doping, the relative density was calculated using the Archimedes method. At first, we have calculated theoretical densities of (Mg1-xCox)TiO3 ceramics using
V N
ZM
A theo =
ρ (5.2)
where Z is the number of atoms per unit cell, M is the molecular weight (g/mol), NA is the Avogadro number (6.023x1023 atoms per mol), and V is the volume of the unit cell (in cm3).
The theoretical densities of pure and Co - doped MTO ceramics are 3.89, 3.89, 3.90, 3.91, 3.92, and 3.93 gm/cm3, respectively.
Figure 5.7 shows the variations in relative densities of (Mg1-xCox)TiO3 (x = 0.00 - 0.07) ceramics as a function of sintering temperature. The relative density increases with increasing sintering temperature up to 1200oC and decreases slightly for the samples sintered at 1250oC. The maximum relative density of 97.26% is obtained for x = 0.05 sintered at 1200oC for 3 h and is attributed to the reduction in porosity, increase in average grain size and uniform microstructure. The decrease in relative densities of the samples with x = 0.07 may be due to the presence of finite amount of secondary phase. The obtained relative density values were in the range of 82.40 - 97.26% for all the samples sintered in the temperature range of 1100 – 1250oC. It is important to note that the processing temperature of MTO ceramics is reduced from 1350oC to 1200oC and sintering temperature is much lower as compared to those reported temperatures for the chemical processes [6, 28].
Figure 5.7: Variations in relative density as a function of sintering temperature for different Co concentrations.
This can be attributed to the use of finer initial particles (see Figure
understand as follows: Nanoparticles have larger surface area resulting higher surface energy, which promotes the sintering process significantly [
the sintering velocity depends upon the nature of the powder, particle size and
temperature. Nanoparticles exhibit distinctive contact necks in the powder and form different inter particle boundaries. Therefore, at lower
mechanisms would be active as a result of the increased sintering velocity, leading to a maximum relative densitiy and larger uniform grain size
density of (Mg1-xCox)TiO3 ceramics increased with be understood from the fact that
uniform grain growth. To understand our results careful analysis using surface area analyzer.
increases with increasing x mol% and the values are in the range of 13.49 increase in surface area certainly supports the enhancement of densification at temperatures. For the samples with
secondary phase. The relative density values and the shrinkage % for the
= 0.00 - 0.07) ceramics sintered at 1200
shrinkage values propose that these samples are also promising for the multilayer ceramic capacitor technology.
: Variations in relative density as a function of sintering temperature for different
This can be attributed to the use of finer initial particles (see Figure
understand as follows: Nanoparticles have larger surface area resulting higher surface energy, which promotes the sintering process significantly [29]. Furthermore, it is
the sintering velocity depends upon the nature of the powder, particle size and
. Nanoparticles exhibit distinctive contact necks in the powder and form different inter particle boundaries. Therefore, at lower sintering temperature, most of the sintering mechanisms would be active as a result of the increased sintering velocity, leading to a maximum relative densitiy and larger uniform grain size [30]. It is also observed that relative
ceramics increased with x concentration up to x = be understood from the fact that Co doping forms a solid solution with MgTiO
understand our results carefully, we have carried out surface area analyzer. It is observed that the surface area of the powder
mol% and the values are in the range of 13.49 – increase in surface area certainly supports the enhancement of densification at
For the samples with x > 0.05, density starts decreasing due to the presence of secondary phase. The relative density values and the shrinkage % for the (Mg
0.07) ceramics sintered at 1200oC are given in Table 5.2. The obtained higher shrinkage values propose that these samples are also promising for the multilayer ceramic : Variations in relative density as a function of sintering temperature for different
This can be attributed to the use of finer initial particles (see Figure 5.2(b)) and understand as follows: Nanoparticles have larger surface area resulting higher surface energy, Furthermore, it is well known that the sintering velocity depends upon the nature of the powder, particle size and sintering . Nanoparticles exhibit distinctive contact necks in the powder and form different , most of the sintering mechanisms would be active as a result of the increased sintering velocity, leading to a It is also observed that relative x = 0.05. This can solid solution with MgTiO3 and promotes ly, we have carried out surface area area of the powder 17.87 m2/g. This increase in surface area certainly supports the enhancement of densification at lower sintering 0.05, density starts decreasing due to the presence of (Mg1-xCox)TiO3 (x The obtained higher shrinkage values propose that these samples are also promising for the multilayer ceramic
Table 5.2: Shrinkage percentage, relative density, measured microwave dielectric constant, dielectric constant corrected for porosit
sintered at 1200oC.
Co Content (x)
Shrinkage (%)
Relative
0.00 20.47
0.01 20.96
0.03 20.57
0.05 21.73
0.07 20.70