THE MECHANICAL BEHAVIOR OF LANTHANUM COBALTITE-BASED
PEROVSKITES WITH A MIXED ION-ELECTRON CONDUCTIVITY
AT DIFFERENT TEMPERATURES
and N. Orlovskaya
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 10, pp.2–8,October, 2001.
The mechanical behavior of a perovskite-type ceramic based on partially substituted lanthanum cobaltites is
studied over a wide temperature range. The La
composite is shown to be the most inelastically de
formable, high-strength, and crack-resistant. In perovskites, the brittleness can be considered as a measure of
both inelasticity and ferroelasticity. The perovskites are tested for deformability using bending and indenta
tion techniques, and an analogy in the results obtained by the two techniques is noted. Specific features of the
fracture of perovskites tested by the Vickers indentation method are discussed. The crack resistance and
stress-strain diagrams of the La
composite are studied as a function of temperature. Fractographic
test data are used to analyze the results obtained.
At present, environment-friendly and efficient technolo-
gies are being put into practice at an ever-increasing rate —
and for their adequate implementation, new, advanced mate
rials are needed. As an example, one may cite the direct con
version of fuel energy to electrical energy using ceramic fuel
cells, the ion-mediated separation of oxygen from air, and
other innovative high-temperature electrochemical pro
cesses. Ceramic with its high ion-electron conductivity —
the most needed material for such operations — along with
performing as an efficient engineering component exposed to
thermal and mechanical loading conditions — must simulta
neously play the role of a structural material. Perovskites of
the type LaCoO
 are candidate materials for those pur
poses and hold promise for fabricating membranes in the
high-temperature separation of oxygen from air, the cathodes
of ceramic fuel cells, etc. . Our goal in the present work
was to study the mechanical behavior of such a ceramic.
CHARACTERIZATION OF PEROVSKITES
Perovskites are ceramic materials with the general for
 (where A is a monovalent or
divalent metal and B is a tetravalent or pentavalent metal)
exhibiting either a crystalline or a domain structure. A spe-
cific feature of these structurally unstable materials is their
ferroelectric polarization and ferroelasticity  and their
ability to undergo phase transformation of the first or second
kind  that cause a change not only in the crystalline or do
main structure but also in the electric phase state. Perovskites
can undergo an energy-absorbing switching (rotation) of
ferroelastic domains  (this effect has been studied in ZrO
) and a transition from the dielectric to the metallic state
(the familiar Mott transition ) that produces a drastic rear
rangement of the electronic spectrum of metals.
Perovskites, owing to their unique physical properties,
have for a long time found numerous uses in technology .
In view of the fact that the electronics industry was the main
consumer of these materials, the focus was on the study of
their electrophysical properties. It is only the use of perov
skites as piezoelectrics that has excited an interest in the
study of their mechanical properties. In fact, this state of
things has continued to the present day despite the results of
a feasibility analysis that predicted an increase in practical
importance of these characteristics in certain perovskites .
The range of works concerned with the study of the mechani
cal behavior of perovskites is rather modest (for example,
moduli of elasticity , strength , crack resistance 
and other characteristics [13, 14] have been considered).
Refractories and Industrial Ceramics Vol. 42, Nos. 9 – 10, 2001
Institute for Problems of Strength, Kiev, Ukraine; Drexel Univer
sity, Philadelphia, Pennsylvania, U.S.A.
1083-4877/01/0910-0341$25.00 © 2001 Plenum Publishing Corporation