472
H. Klym et al.
These transformations were in good agreement with positron trapping rate in
defects (Table 29.3, Fig. 29.8). Nevertheless, there were no significant changes in
τ av. , τ b , τ 2 /τ b , and (τ 2 − τ b ). In all cases, the same type of positron trapping
center is formed. The character size of these extended positron traps near grain
boundaries estimated due to (τ 2 − τ b ) difference is close to single-double atomic
vacancies [16].
29.5 Conclusions
Structural peculiarities of temperature-sensitive Cu 0.4 Co 0.4 Ni 0.4 Mn 1.8 O 4 ceramics
caused by micro- and macro-modifications as well as Cu 0.1 Ni 0.8 Co 0.2 Mn 1.9 O 4
ceramics related with monolithization processes were studied using traditional
structural methods in comparison with PAL technique. It is shown that adequate
characterization methodology for free-volume defects in the modified spinel ceramics can be developed in terms of positron trapping model. The first component
on the positron lifetime spectra has shown microstructure specificity of the spinel
ceramics with octahedral and tetrahedral cation vacancies. The extended defects
near grain boundaries (voids) are reflected by the second component. The small third
component is due to “pick-off” annihilation of o-Ps in the intergranular nanopores.
The observed o-Ps lifetime ∼1.8 ns is related to the nanopores with radius of
∼2.7 nm based on classic Tao-Eldrup equation. The reported data gives additional
information to Hg-porosimetry and SEM results.
In the case of Cu 0.1 Ni 0.8 Co 0.2 Mn 1.9 O 4 ceramics, the results of PAL measurements confirm the interphase mass transfer processes caused by monolitization
processes in ceramics during technological modification and owing to optimal
content of additional NiO phase. Obtained results are in well agreement with
microstructural X-ray diffractometry and electron microscopy data, confirming the
structural changes in these ceramics caused by their technological modification.
Acknowledgments H. Klym thanks the Ministry of Education and Science of Ukraine for support
(grant No 0116 U004411).
References
1. Salomao R, Bôas MOV, Pandolfelli VC (2011) Porous alumina-spinel
ceramics
for
high
temperature
applications.
Ceram
Int
37(4):1393–1399
https://doi.org/10.1016/j.ceramint.2011.01.012
2. Feltz A, Pölzl W (2000) Spinel forming ceramics of the system Fe x Ni y Mn 3–x–y O 4
for high temperature NTC thermistor applications. J Eur Ceram Soc 20(14):2353–2366
https://doi.org/10.1016/S0955-2219(00)00140-0
3. Feteira A (2009) Negative temperature coefficient resistance (NTCR) ceramic
thermistors: an industrial perspective. J Am Ceram Soc 92(5):967–983.
https://doi.org/10.1111/j.1551-2916.2009.02990.x
H. Klym et al.
These transformations were in good agreement with positron trapping rate in
defects (Table 29.3, Fig. 29.8). Nevertheless, there were no significant changes in
τ av. , τ b , τ 2 /τ b , and (τ 2 − τ b ). In all cases, the same type of positron trapping
center is formed. The character size of these extended positron traps near grain
boundaries estimated due to (τ 2 − τ b ) difference is close to single-double atomic
vacancies [16].
29.5 Conclusions
Structural peculiarities of temperature-sensitive Cu 0.4 Co 0.4 Ni 0.4 Mn 1.8 O 4 ceramics
caused by micro- and macro-modifications as well as Cu 0.1 Ni 0.8 Co 0.2 Mn 1.9 O 4
ceramics related with monolithization processes were studied using traditional
structural methods in comparison with PAL technique. It is shown that adequate
characterization methodology for free-volume defects in the modified spinel ceramics can be developed in terms of positron trapping model. The first component
on the positron lifetime spectra has shown microstructure specificity of the spinel
ceramics with octahedral and tetrahedral cation vacancies. The extended defects
near grain boundaries (voids) are reflected by the second component. The small third
component is due to “pick-off” annihilation of o-Ps in the intergranular nanopores.
The observed o-Ps lifetime ∼1.8 ns is related to the nanopores with radius of
∼2.7 nm based on classic Tao-Eldrup equation. The reported data gives additional
information to Hg-porosimetry and SEM results.
In the case of Cu 0.1 Ni 0.8 Co 0.2 Mn 1.9 O 4 ceramics, the results of PAL measurements confirm the interphase mass transfer processes caused by monolitization
processes in ceramics during technological modification and owing to optimal
content of additional NiO phase. Obtained results are in well agreement with
microstructural X-ray diffractometry and electron microscopy data, confirming the
structural changes in these ceramics caused by their technological modification.
Acknowledgments H. Klym thanks the Ministry of Education and Science of Ukraine for support
(grant No 0116 U004411).
References
1. Salomao R, Bôas MOV, Pandolfelli VC (2011) Porous alumina-spinel
ceramics
for
high
temperature
applications.
Ceram
Int
37(4):1393–1399
https://doi.org/10.1016/j.ceramint.2011.01.012
2. Feltz A, Pölzl W (2000) Spinel forming ceramics of the system Fe x Ni y Mn 3–x–y O 4
for high temperature NTC thermistor applications. J Eur Ceram Soc 20(14):2353–2366
https://doi.org/10.1016/S0955-2219(00)00140-0
3. Feteira A (2009) Negative temperature coefficient resistance (NTCR) ceramic
thermistors: an industrial perspective. J Am Ceram Soc 92(5):967–983.
https://doi.org/10.1111/j.1551-2916.2009.02990.x