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INTERNAL FRICTION IN PARTIALLY STABILIZED
ZIRCONIA
K. Matsushita, T. Okamoto, M. Shimada
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C10, supplement au n012, Tome 46, decembre 1985 page C10-549
INTERNAL FRICTION IN PARTIALLY STABILIZED ZIRCONIA
K. MATSUSHITA, T. OKAMOTO AND M. SHIMADA'
The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka, Japan
'Department of Applied Chemistry, Faculty of Engineering, Tohoku University, Sendai, Miyagi, Japan
Abstract- Internal friction was measured by the flexural vibra- tion method at 1-6 KHz. Internal friction peaks in partially stabilized zirconia with Y2O3 or Nd2O3 are observed at about 200°C. The intensity of these peaks increases with increasing Y2O3, La203, Nd2O3, La203 or Ce02 content. Both internal frlction peaks appearing on heating and on cooling are revers- ible without temperature hysteresis. From the frequency dependence of the peak temperature, the activation energy for the relaxation relating to the peak is 80-90 ~ ~ / m o l . It is concluded that these peaks are associated with stress induced oxygen ion movement.
Introduction- Solid electrolytes from zirconia based solid solutions are used as electrochemical cells to be applied to fuel cells, oxygen monitors and others. In these cases, ionic conductivity of oxygen ions is uti1ized.l ) r2) At room temperature the cubic phase of
zirconia is stabilized partially or perfectly by containing CaO, MgO, Y2O3 or Ce02. Partially stabilized zirconia (PSZ) consisting of cubic and metastable tetragonal phases is superior in strength as compared with perfectly stabilized zirconia.3) The addition of CaO, MgO or Y203 into Zr02 replaces Zr atoms with 4 valences in
zirconia by Ca or Mg atoms with 2 valences or Y atoms with 3 valences. As a result, some oxygen ions and vacancies are formed in zirconia4). The present authors discuss the relation between the relaxation strength and the content of additives, such as Y2O3, Ce02, La203 and.Nd203, and the activation energy for the diffusion of oxygen ions in partially stabilized zirconia,
C10-550
JOURNAL
DE
PHYSIQUE
Experimental Procedure- young's modulus and internal friction of PSZ are measured by the flexural vibration method in the range of 1 to 6 KHz and by the free decay method in the temperature range of room temperature to 700'~. Zirconia ceramics with additives were sintered under a pressure-less condition at 1500°C for 2 hours in air. The chemical compositions of zirconia ceramics are shown in Table 1.
Temperature dependences of internal friction and Young's modulus were measured on the following condition. Heating and cooling rates of the
specimens were 3O~/min in a nitrogen atmosphere and the maximum strain amplitude was about 5x1
o - ~ .
Frequency dependences of internalfriction and young's modulus were also measured.
Table 1 Characteristics of zirconia ceramics
Sample Composition phase*) ERT E ~ O O O C Q-l 1 /~(AE/E) (GPa) (GPa) (x10-3, (x10-3,
-
A 2mol%Y203-Zr02 T 207 180 15 22.5 B 3rnol%Y203-Zr02 T+C 205 117 27 28.0 C 8mol%Ce02+2mol% C 107 188 4.2 6.3 (La203,Nd203)-Zr02 D 12mol%Ce0~+3rnol% C 202 184 9.5 10.5 (La203,Nd203)-Zr02 * ) T; tetragonal C; cubicsintering condition; 1500 C for 2h in Air
Results
and
Discussion- Young's moduli of the samples at roomtemperature (ERT) and at 4 0 0 ' ~ are listed in Table 1. The moduli of all the samples at room temperature are nearly equal, The moduli at 400'~ show that sample B has the smallest val'ue, 177 GPa, and that sample C has the largest value, 188 GPa. This difference is associ- ated with the relaxation strength. Temperature dependences of
internal friction and Young's modulus measured at about 1 KHz for all the samples are shown in Fig.1. The internal friction vs temperature curves for all the samples show a large peak around 200'~ and the width at half the peak height is 100-120'~. Both internal friction peaks appearing on heating and on cooling are reversible without temperature hysteresis. It has been known that zirconia with a small amount of Y2O3, La203 or Nd2O3 transforms from tetragonal
structure to monoclinic one during annealing5). Since the internal friction peaks in the samples at about 200'~ on heating and on cooling are perfectly reversible, the peaks should not be concluded to be associated with the phase transformation. The values of the internal friction peak (Q-lp) and 1 /2(
A
E/E)of each sample are listed inT a b l e 2 A c t i v a t i o n e n e r g y of i n t e r n a l f r i c t i o n peak o b t a i n e d bv t h e ~ e a k s h i f t method
Sample F r e q . ( H z ) Peak Temp,('C) A c t i v . ~ n e r g y ( ~ ~ / m o l ) F r e q . F a c t o r
(s-1)
930 1 7 8
A 261 0 203 69.322.0 5 . 9 ~ 1
o1
5850 225
Fig. 1 Fig. 2
Temperature dependences of internal Internal friction vs temperature friction and Young's moduli in curves measured at two frequencies. sample A,B,C and D.
Open mark ; on heating Closed mark; on cooling
( 2 0 - 5 5 2 JOURNAL DE PHYSIQUE
The internal friction vs temperature curves in 2 mol%Y~O3- 21-02 at two frequencies are shown in Fig.2. The internal friction peak temperatures are 178'~, 203'C and 225'~ at resonant frequencies of 930 Hz, 2610 Hz and 5850 Hz, respectively. The frequency depend- ences of internal friction peak temperature in samples A, B and D are listed in Table 2. The activation energy calculated from the each slope of Q n o - I / T plots is also shown in Table 2. These values of the activation energy are nearlyequal to that of the self diffusion of oxygen ions in zirconia stabilized by calcia.4),6) Internal friction peak height in samples C and D is considerably smaller than that of samples A and B. The former is about one-third of the latter. It was observed from the X-ray diffraction patterns that La203 and
Nd2O3 partially dissolved in the zirconia. Oxygen vacancy concen- tration in zirconia containing La203
or
Nd2O3 has to be the same as that in zirconia with Y2O3 of the same content as the former, because La or Nd atoms nave the same valences as Y atoms. There is no oxygen vacancy in zirconia doped with Ce02 exceptvacancies introduced in a thermally equilibrated state. Therefore, it can be concluded that La203 or Nd2O3 is slightly soluble in
zirconia.
This work was supported by the research project of I.S.I.R. on development of new materials for energy.
References
1) F.K.Moghadam and D.A.Stevenson; J.Am.Cerarn.Soc., =(1982), 213. 2) T.Y.Tien and E.C.Subbard; J.Chem.Physics, ' ~ ( 1 9 6 3 ) ~ 1041. 3) D.Miche1, L.Mazerolles and M.P.Y.Jorba; J.Mat.Sci., x(1983),
261 8.
4) K.Ando ,and Y.Oishi, Ceramics,, =(I 982), 41 2. (in Japanese). 5) C.Pasca1 and P.Duran; J.Am.Ceram.Soc., =(1983), 23.
6 ) W.D.Kingery, J.Papis, M.E.Doty and P.C.Hil1; J.Am.Ceram.Soc., 42 (1959), 393.
