Open Journal of Inorganic Non-Metallic Materials, 2013, 3, 37-42
http://dx.doi.org/10.4236/ojinm.2013.33007 Published Online July 2013 (http://www.scirp.org/journal/ojinm)
Syntheses of Doped-LaCrO3 Nanopowders by
Minkyung Kang, Juyeon Yun, Chiwook Cho, Changyoon Kim, Weonpil Tai*
Fine Chemical and Material Technical Institute, Ulsan Techno Park, Ulsan, Republic of Korea
Received March 28, 2013; revised April 25, 2013; accepted May 9, 2013
Copyright © 2013 Minkyung Kang et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The effects of additives and precipitants on the syntheses of doped LaCrO3 (lanthanum chromites) were studied by
hydrothermal reaction at temperature ranges of 100˚C to 230˚C. LaCrO3 nanopowders were synthesized by hydrother-
mal methods using several types of precipitants such as NaOH, KOH, NH4OH, and NH2CONH2. The influence of Sr,
Ca and Co doping on the lanthanum chromites prepared by hydrothermal method were investigated. The synthesized
nanopowders were characterized by means of XRD, SEM and densitometer. The electrical conductivity of the doped
LaCrO3 was studied at 750˚C in air by a DC four point probe method. The particles size of undoped LaCrO3 nanopow-
der was approximately 100 nm when using KOH as a precipitant. The relative density of lanthanum chromite doped
with calcium and cobalt is over 97%. The highest electrical conductivity of La0.62Ca0.38Co0.18Cr0.82O3 was 32.75 S/cm at
750˚C in air, which is 30 times higher than undoped LaCrO3. The density and electrical conductivity are increased by
doping cobalt and calcium on the LaCrO3.
Keywords: Doped LaCrO3; Hydrothermal Reactions; Interconnects for Solid Oxide Fuel Cell
The interconnect of a SOFC stack electrically and physi-
cally is connected to the anode of one unit cell with the
cathode of the adjacent unit cell in the stack. The inter-
connect can be ceramic or metallic materials. The inter-
connect materials used for SOFC stacks must be elec-
tronically conductive, oxidation resistant, impermeable to
the diffusion of gases, and chemically stable with fuel
cell materials . There are suitable materials, such as
ceramics and metals for interconnect in solid oxide fuel
cell (SOFC). Each material has advantages, but neither is
ideal. Metallic chromium-forming alloys are most com-
monly used, but the formation of chromium-containing
vapor species can lead to poisoning of the cathode after
long operation. The resistance to this degradation can be
improved through a combination of the two materials by
ceramic coating on the metallic interconnect .
Ceramic interconnects based upon ceramic oxides with
perovskite structure have been subject of intensive study
over the past several decades. It was found that only a
few such oxides systems can fulfill the rigorous require-
ments for the interconnect materials in SOFC. Lantha-
num chromites (LaCrO3) is the most common candidate
material since it demonstrates reasonably high electronic
conductivity in both fuel and oxidant atmospheres, mod-
erate stability in the fuel cell environments as well as
fairly good compatibility with other cell components in
terms of phase, microstructure and thermal expansion. In
order to improve the electrical conductivity as well as
modify the thermal expansion coefficient (TEC), LaCrO3
is often doped on lanthanum site, chromium site or both
sites of the perovskite for practical applications. Due to
ionic radius similarity, strontium and calcium tend to
replace La ions whereas magnesium, iron, nickel, copper
and cobalt prefer to take over the site of Cr ions. As a
matter of fact, in SOFC configuration, the doped LaCrO3
is still the most widely used as an interconnect .
Nanotechnology is the key for enhancing the perfor-
mance of fuel cell. It is being used to lower the operating
temperature of solid oxide fuel cells (SOFC). Also it can
improve durability and increase oxygen-ion conductivity
in the low temperature. The interconnect materials pre-
pared using nanopowders in SOFC could be decreased
the sintering temperature due to higher surface area. Also,
it is advantageous for the formation of the dense film to
have high temperature durability .
opyright © 2013 SciRes. OJINM
M. KANG ET AL.
The nanopowders have been synthesized by several
methods such as glycine nitrate process , oxalic salt
method , hydrazine , coprecipitation , and sol-
gel . These chemical processes, however, involve a
subsequent calcination at high temperatures beyond
700˚C, in order to obtain a stable crystalline phase. The
LaCrO3 is suitable for use as an interconnector, due to its
high stability at high temperature. However, it has poor
sinterability. The advantage of hydrothermal method is
easy to control the particle size and shape, and it can be
synthesized at low temperatures as a method of synthesis
of crystalline nanopowders that depends on the solubility
of the material under high pressure.
In this study, we synthesized doped LaCrO3 nano-
powder without secondary phase at low temperatures of
100˚C - 230˚C using hydrothermal method for intercon-
nect materials in solid oxide fuel cell (SOFC). In order to
improve its poor sinterability and electrical properties,
Ca, Sr and Co were doped on lanthanum chromites, the
sintering and electrical properties behaviors were inves-
2.1. Hydrothermal Synthesis and Sintering
The doped LaCrO3 nanopowders were synthesized by
hydrothermal method. All the raw materials were used
reagent grade without purification. The starting materials
were used La(NO3)3·6H2O (Sigma-Aldrich Co., USA),
Cr(NO3)3·9H2O (Sigma-Aldrich Co., USA) and Ca(NO3)2·xH2O
(>98%, Sigma-Aldrich Co., USA), Co(NO3)2·6H2O (>98%,
Sigma-Aldrich Co.), Sr(NO3)2 (>99%, Sigma-AldrichCo.,
USA) as dopants. The highly crystalline LaCrO3 nan-
opowders were prepared under hydrothermal conditions
using several species of precipitants such as urea
(NH2CONH2, Junsei, Chemical Co., Tokyo, Japan), am-
monia (NH4OH, GR, Dae Jung Chemical, Korea), potas-
sium hydroxide (KOH, GR, Dae Jung Chemical, Korea)
and sodium hydroxide (NaOH, GR, Kanto Chemical Co.,
Tokyo, Japan). Aqueous solutions with 0.05 M of
La(NO3)3 to Cr(NO3)3 and dopants (Ca, Sr, Co) were
prepared with deionized water. The several precipitant
aqueous solutions of KOH (0.35 M), NaOH (0.5 M),
NH2CONH (0.25 M), and NH4OH (0.3 M) were pre-
pared. The nitrate salts was added slowly in deionized
water with precipitants. The mixture was poured into a
teflon–liner in autoclave after ultrasonic treatment for
30min. The autoclave was heated at various temperature
of 100˚C - 230˚C for a reaction time between 8 - 30 h.
After the hydrothermal reaction, the nanopowder was wash-
ed with distilled water using centrifuge (FLETA5, Hanil),
and then, dried in an oven at 260˚C - 280˚C for 7 h. The
undoped lanthanum chromite (LaCrO3) and doped lanthan-
um chromite (La1–xMxCr1–yCoyO3) with M (La1–xMxCrO3,
M = Ca, Sr) were synthesized by hydrothermal methods
at low temperature (100˚C - 230˚C). In the present study, x
is from 0 to 0.4 and y is from 0 to 0.2.
The sintering of the nanopowders was conducted by a
conventional firing in air. The nanopowders was mixed
with poly vinyl alcohol as a binder and pressed into
quadrilateral sheet with a diameter of 10 mm at 10 MPa,
and then compressed by press (CARVER, 385L-0) at 1
psi for 5 min. The pellets were sintered in a covered alu-
mina crucible at 1200˚C - 1500˚C for 1 to 5 h in air. The
pellet was heated at a constant heating rate of 5˚C/min up
to the sintering temperature.
In order to determine the crystalline phase and the lattice
parameter constants of the synthesized nanopowder, X-
ray diffraction analyses were carried out. The crystal
structures of the sintered specimens were examined using
an X-ray diffractometer (XRD, D/MAX 2500-V/PC,
Rigaku, Japan) with graphite-monochromatized Cu Ka
radiation at 40 kV and 100 mA. Diffraction patterns were
taken from 10 to 80˚ at a scanning speed of 4˚/min.
Morphological aspects of the nanopowders were exam-
ined by scanning electron microscope (FE-SEM, Supra
40, Zeiss) equipped with an energy dispersive X-ray
spectroscopy (EDX). The particle size was measured by
particle size analyzer (PSA, Beckman Coulter LS 13
320). Moreover, the relative densities of the hydrother-
mally synthesized nanopowders were calculated from the
densitometer. The electrical conductivity of the samples
was studied at 750˚C in air by a standard DC four point
3. Result and Discussion
The highly crystalline LaCrO3 nanopowders were pre-
pared by hydrothermal method using several species of
precipitants such as urea, ammonia, potassium hydroxide
and sodium hydroxide. Aqueous solutions with 0.05 M
of La(NO3)3 to Cr(NO3)3 and dopants (Ca, Sr, Co) were
prepared with deionized water. The aqueous solutions of
precipitants which are KOH of 0.35 M, NaOH of 0.5 M,
NH2CONH2 of 0.25 M and NH4OH of 0.3 M were pre-
pared. Table 1 shows the optimal hydrothermal synthesis
condition of LaCrO3, according to the species of precipi-
tants. Figure 1 shows X-ray diffraction patterns of the
reaction product after hydrothermal reaction at the sev-
eral conditions. LaCrO3 phase formed when it treated
hydrothermally in the autoclave at 250˚C for 30 h using
urea and ammonia as the precipitant. However, precipi-
tants such as KOH and NaOH result in the complete
transformation to the perovskite structure of ABO3 type
at the low temperature, which is the reaction temperature
of 220˚C to 230˚C. The XRD pattern of the specimen
Copyright © 2013 SciRes. OJINM
M. KANG ET AL. 39
The optimal hydrothermal syntheses conditions of
NH2CONH2 1 : 1 : 5 30 250
NH4OH 1 : 1 : 6 30 250 LaCrO3
KOH 1 : 1 : 7 24 220 LaCrO3
NaOH 1 : 1 : 10 24 230 LaCrO3
Figure 1. X-ray diffraction patterns of synthesized LaCrO3
nanopowder using several precipitants by hydrothermal
method; (a) 0.5 M NaOH, at 230˚C for 24 h; (b) 0.35 M
KOH, at 220˚C for 24 h; (c) 0.25 M Urea, at 250˚C for 30 h;
(d) 0.3 M Ammonia, at 250˚C for 30 h.
prepared from the different ratio of KOH with nitrate
precursor shows that it occurs small amounts of secon-
dary phases, such as La(OH)3 and La(CO3)OH. Small
amounts of secondary phases were only observed when
the NH2CONH2 of 0.25 M was used as a precipitant. The
preferential formation of La(CO3)OH phase might be
attributed to CO2 absorption in alkaline media . The
presence of a small amount of La(OH)3 might be due to
an incongruent dissolution behavior of La3+ in alkaline
Figure 2 shows the morphology of hydrothermally
synthesized LaCrO3 nanopowders observed by SEM and
the particle size measured by PSA. It shows some dif-
ferences on particle shape and size when various precipi-
tants were used. When NaOH of 0.5 M as a precipitant
was used, the particle size was approximately 230 nm
and it exhibits clusters of round-shaped particles as
shown in Figure 2(a). The LaCrO3 nanopowder using
KOH of 0.35 M has a regular morphology, which is oval
shape and homogeneous size distribution as shown in
Figure 2(b), the average particle size was less than 100
nm. The LaCrO3 nanopowder, using NH2CONH 2 of 0.25
M had irregular morphology and wide particle size dis-
tribution in which particle size was about 380 nm, as
shown in Figure 2(c). In contrast, the LaCrO3 nanopow-
ders, using NH4OH of 0.3 M formed plate type and
small particle agglomerated together with larger cluster.
The particle size was about 280 nm as shown in Figure
2(d). The shape of the nanoparticles seems to be affected
by species of the precipitants.
We also synthesized the doped lanthanum chromites
(La1–xMxCr1–yCoyO3, M = Ca, Sr) by hydrothermal reac-
tion at 220˚C. Potassium hydroxide was used as a pre-
cipitant, and then the mole ratio of KOH to nitrates pre-
cursor was 7:1 in all composition. The prepared speci-
mens were La1– x MxCr 1–yCoyO3 with x = 0 to 0.4 and y =
0 to 0.2. The nitrate precursor was mixed in distilled wa-
ter. Figure 3 shows the X-ray diffraction patterns of
doped LaCrO3 nanopowders. Figure 3(a) shows X-ray
diffraction patterns of the Ca-doped LaCrO3 nanopow-
ders. Most of Ca-doped LaCrO3 nanopowders were ob-
tained crystalline phase, but the La0.85Ca0.15CrO3 was
observed a small amount of secondary phase, CaCrO4.
Generally, the X-ray diffraction pattern peaks is shifted
to higher angle with increasing calcium concentration. It
could be decreased the lattice constants of perovskite
structure because the Ca ions is substituted to La ions,
due to the Ca ionic radius (0.99Ả) smaller than La
(1.15Ả) . Figure 3(b) shows the X-ray diffraction
patterns of Co-doped LaCrO3 nanopowders. The cobalt is
added to improve the sintering process. It is observed a
slight increase of the peak intensity by increasing the
amount of Co. It indicates that Co is substituted to Cr in
solid solution . Figures 3(c) and (d) show X-ray dif-
fraction patterns of (Sr,Co)-doped LaCrO3, which de-
Figure 2. SEM micrographs of synthesized LaCrO3 nano-
powders using several precipitants by hydrothermal me-
thod. (a) 0.5 M NaOH, at 230˚C for 30 h; (b) 0.35 M KOH,
at 220˚C for 24 h; (c) 0.25 M Urea, at 250˚C for 30 h; (d) 0.3
M Ammonia, at 250˚C for 30 h.
Copyright © 2013 SciRes. OJINM
M. KANG ET AL.
Figure 3. X-ray diffraction patterns of doped LaCrO3 nano-
powders; (a) La1–xCaxCrO3 (0 ≤ x ≤ 0.4); (b): La1–xCax
Cr1–yCoyO3 (x = 0.38, 0 ≤ y ≤ 0.2); (c): La1–xSrxCrO3 (0 ≤ x ≤
0.2); and (d) La1–xSrxCr1–yCoyO3 (x = 0.2, 0 ≤ y ≤ 0.2).
pends on the amount of doping precursor. Sr-doped La-
CrO3 can synthesize homogeneous nanopowders at rela-
tively low temperature. Additionally, secondary phases
such as LaCrO4, SrCrO4 and Sr(NO3)2 was observed. It is
possible to the solubility limits of Sr in the LaCrO3. La-
CrO4 can be considered as an intermediate phase in the
lanthanum chromites [14,15].
We studied the influence of additives, which are cal-
cium, strontium and cobalt, for the densification behavior
of the doped LaCrO3 nanopowders. The relative densities
of doped LaCrO3 sintered at temperature ranges of
1200˚C to 1500˚C are shown in Figure 4. The relative
density of the undoped LaCrO3 is 74.9% at 1400˚C. The
densities of doped LaCrO3 were increased with increas-
ing the sintering temperature. The density of all the
A-site doped LaCrO3 was increased at all the temperature
ranges. The density of (Ca,Co)-doped LaCrO3 was higher
than (Sr,Co)-doped LaCrO3. The La0.62Ca0.38Co 0.18Cr0.82O3
sintered at 1200˚C for 4 h exhibits the highest density.
When the sintering temperature increased over 1500˚C,
the relative density was hardly change because the doped
LaCrO3 was fully sintered at 1400˚C for 4 h. The sinter-
ing temperature of La0.62Ca0.38Co0.18Cr0.82O3 is approxi-
mately 200˚C lower than undoped LaCrO3 samples, due
to enhanced sinterability by doping Ca and Co [16-18].
Figure 5 shows the microstructures of the nanopow-
ders and sintered doped LaCrO3 nanopowders at the sev-
eral conditions. Figure 5(a) shows micrograph of La-
CrO3 nanopowder and the particle size was ~100 nm.
Figure 4(b) shows the fracture surface of the LaCrO3
sintered at 1400˚C for 4 h. Figure 5(c) shows the micro-
structure of the La0.62Ca0.38Co0.18Cr0.82O3 nanopowder
which is the optimum composition, and the particle size
Copyright © 2013 SciRes. OJINM
M. KANG ET AL. 41
Figure 4. Relative density of doped LaCrO3 at the several
Figure 5. SEM micrographs of doped LaCrO3; (a) LaCrO3
nanopowder; (b) Fracture surface of (a) sintered at 1400˚C
for 4 h; (c) La0.62Ca0.38Co0.18Cr0.82O3 nanopowder; (d) Frac-
ture surface of (c) sintered at 1200˚C for 4 h; (e)
La0.8Sr0.2Co0.15Cr0.85O3 nanopowder; and (f) Fracture sur-
face of (e) sintered at 1500˚C for 4 h.
was about 80 nm. Figure 5(d) shows the fracture surface
of La0.62Ca0.38Co0.18Cr0.82O3 sintered at 1200˚C for 4 h.
Figure 5(e) shows microstructure of the La0.8Sr0.2Co0.15-
Cr0.85O3 nanopowder and the particle size was ~200 nm.
Figure 5(f) shows the fracture surface of the La0.8Sr0.2-
Co0.15Cr0.85O3 sintered at 1500˚C for 4 h. When sintered
at over 1200˚C, the doped LaCrO3 were densely sintered.
It indicated that sintering density is dependent on the
additives and sintering temperature.
Figure 6 shows the electrical conductivity of doped
LaCrO3 measured at 750˚C in air. The electrical conduc-
tivity increased in all the doped LaCrO3. The La0.62Ca0.38-
Co0.18Cr0.82O3 sintered at 1200˚C had maximum conduc-
tivity of 32.73 S/cm at 750˚C in air, which is about 30
times as high as that of undoped LaCrO3.
LaCrO3 nanopowders were synthesized by hydrothermal
method at temperature ranges of 100˚C to 230˚C for 8 -
30 hrs. The average particle size of undoped LaCrO3 was
approximately 80 nm when the KOH was used as a pre-
cipitant. The particles size of (Sr, Co)-doped LaCrO3
nanopowder was approximately 200 nm. The (Ca,Co)-
doped LaCrO3 nanopowders exhibit improved crystalline
compared with the undoped LaCrO3 nanopowders. The
undoped LaCrO3 nanopowder has a poor sinterability in
air, but a highly dense La0.62Ca0.38Co0.18Cr0.82O3 was ob-
tained by doping Ca and Co. The sintering temperature
of La0.62Ca0.38Co0.18Cr0.82O3 is about 200˚C lower than
undoped LaCrO3. The relative density increased over
97% by doping Ca on perovskite A site and Co on perov-
skite B site. The electrical conductivity of La0.62Ca0.38-
Co0.18Cr0.82O3 was 32.73 S/cm. However, Sr- doped lan-
thanum chromite nanopowders were observed the sec-
ondary phases of LaCrO4 and SrCrO4 for all the compo-
sitions. The electrical conductivity of La0.8Sr0.2Co0.15-
Cr0.85O3 was 29.4 S/Cm at 750˚C. The density and elec-
trical conductivity were increased by doping calcium and
cobalt on the LaCrO3. The (Ca, Co)-doped LaCrO3 is
adequate for applications as an interconnector in SOFC.
This research was financially supported by the Ministry
of Knowledge and Economy, Korea (grant no. 10037
Figure 6. Electrical conductivity of doped LaCrO3 meas-
ured at 750˚C in air.
Copyright © 2013 SciRes. OJINM
M. KANG ET AL.
Copyright © 2013 SciRes. OJINM
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