Temperature-dependent structures of proton-
conducting Ba(Zr0.8-xCexY0.2)O2.9 ceramics 
by Raman scattering and x-ray diffraction
Authors: C.-S. Tu, R. R. Chien, V. Hugo Schmidt, S. C. 
Lee, and C.-C. Huang
This is an author-created, un-copyedited version of an article published in [insert name of journal]. IOP 
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C.-S. Tu, R.R. Chien, V.H. Schmidt, S.C. Lee, and C.-C. Huang, “Temperature-dependent structures of 
proton-conducting Ba(Zr0.8-xCexY0.2)O2.9 ceramics by Raman scattering and x-ray diffraction,” 
Journal of Physics: Condensed Matter 24, 155403 (6 pp.) (2012), doi: 
10.1088/0953-8984/24/15/155403.
Made available through Montana State University’s ScholarWorks 
scholarworks.montana.edu 
Temperature-dependent structures of
proton-conducting
Ba(Zr0.8−xCexY0.2)O2.9 ceramics by
Raman scattering and x-ray diffraction
C-S Tu1,2, R R Chien3, V H Schmidt3, S C Lee2 and C-C Huang2
1 Graduate Institute of Applied Science and Engineering, Fu Jen Catholic University, Taipei 24205,
Taiwan
2 Department of Physics, Fu Jen Catholic University, Taipei 24205, Taiwan
3 Department of Physics, Montana State University, Bozeman, MT 59717, USA
Abstract
In situ temperature-dependent micro-Raman scattering and x-ray diffraction have been
performed to study atomic vibration, lattice parameter and structural transition of
proton-conducting Ba(Zr0.8−xCexY0.2)O2.9 (BZCY) ceramics (x = 0.0–0.8) synthesized by
the glycine–nitrate combustion process. The Raman vibrations have been identified and their
frequencies increase with decreasing x as the heavier Ce4+ ions are replaced by Zr4+ ions.
The main Raman vibrations of Ba(Ce0.8Y0.2)O2.9 appear near 305, 332, 352, 440 and
635 cm−1. The X–O (X = Ce, Zr, Y) stretching modes are sensitive to the variation of Ce/Zr
ratio. A rhombohedral–cubic structural transition was observed for x = 0.5–0.8, in which the
transition shifts toward higher temperature as cerium increases, except for Ba(Ce0.8Y0.2)O2.9.
A minor monoclinic phase possibly coexists in the rhombohedral matrix for x = 0.5–0.8. The
lower-cerium BZCYs (x = 0.0–0.4) ceramics do not exhibit any transition in the region of
20–900 ◦C, indicating a cubic phase at and above room temperature.
(Some figures may appear in colour only in the online journal)
and power density in BZCY-based ceramics as functions
of cerium/zirconium ratio, glycine–nitrate ratio, sintering
parameter and temperature [5–8]. These power densities
are competitive with those achieved by O-SOFCs with
oxygen-ion-conducting electrolytes. H-SOFCs have two
advantages over O-SOFCs, based on the fact that on the
anode side there is only hydrogen inflow, with no steam
outflow. First, higher fuel utilization can be achieved because
there is no loss of fuel flowing out with the steam exhaust
gas. Second, anode-supported cells having a relatively thick
anode are desirable because the anode has a strong metal
framework, and there is much less fuel pressure loss through
the anode passages in H-SOFCs because there is no steam
counterflow.
1. Introduction
Perovskite-type (Ba, Sr, Ca)(Zr, Ce)O3 oxides exhibit good 
protonic conduction under hydrogen-containing atmosphere 
at elevated temperature, and are promising for applications 
of proton-conducting solid oxide fuel cells (H-SOFCs), 
hydrogen separation membranes, hydrogen pumps, hydrogen 
sensors and steam electrolyzers for hydrogen production [1, 
2]. For instance, hydrogen-fueled H-SOFCs with BZCY 
electrolytes made by Yang et al [3] achieved a power 
density of 700 mW cm−2 at the relatively low temperature 
of 700 ◦C, and BZCY-based cells made by Meng et al [4] 
reached 371 mW cm−2. Our group has been investigating 
thermal stability (in CO2 atmosphere), ionic conductivity
Cerate-based proton conductors have a high ionic
conductivity but exhibit poor chemical stability in CO2-
and H2O-containing atmosphere at elevated temperature [9].
Although zirconate-based proton conductors have lower
ionic conductivity, they show good thermal and mechanical
stabilities [10]. The previous results suggested that proton-
conducting solid solutions between cerate and zirconate
may have both high proton conductivity and good chemical
stability [11, 12]. AIIBIVO3-based proton conductors have
been doped in the B site by lower valence elements, typically
Y3+ (RIII = 0.9 A˚) or trivalent rare earth metal cations,
creating oxygen vacancies. Subsequent exposure to humid
atmospheres is presumed to lead to the incorporation of
protons, resulting in proton conduction [13, 14].
BaCeO3 has a transition sequence of orthorhombic
(Pnma)–orthorhombic (Imma)–rhombohedral (R3c)–cubic
(Pm3¯m) at 290, 400 and 900 ◦C, respectively [15]. Different
phases were reported at room temperature for BaCeO3
prepared by various methods, including orthorhombic,
tetragonal, pseudocubic and cubic phases [16]. This type of
perovskite can crystallize in various structures, depending on
processing method and sintering condition. BaZrO3 is cubic
at and above room temperature [17]. Yttria-stabilized zirconia
(YSZ) has a disordered cubic face-centered fluorite-type
lattice in which the Zr4+ cations are partially substituted by
the Y3+ cations and one oxygen vacancy per pair of Y3+
ions is generated. The neutron diffraction result suggested a
rhombohedral R3¯c phase for Ba(Ce0.8Y0.2)O2.9 (BCY82) at
room temperature [18]. A coexistence of rhombohedral and
monoclinic phases was proposed for BCY82 [19].
There is not much knowledge of the temperature-
dependent phase diagram regarding the proton-conducting
Ba(Zr,Ce,Y)O3−δ ceramics even though the mixed com-
pounds with the addition of yttrium are important for fuel
cell and hydrogen separation membrane applications. The
thermal structural property is an important factor for using
proton-conducting Ba(Zr,Ce,Y)O3−δ ceramics in fuel cells.
In this work, temperature-dependent x-ray diffraction (XRD)
and micro-Raman scattering were employed to investigate
atomic vibrations, lattice parameters of the unit cell and
structural transitions of Ba(Zr0.8−xCexY0.2)O2.9 ceramic
powders in an argon-containing environment.
2. Experimental details
The glycine-to-nitrate (G/N) combustion process was used
to synthesize nanosized Ba(Zr0.8−xCexY0.2)O2.9 (BZCY)
ceramic powders as a function of cerium-to-zirconium ratio
(x = 0.0–0.8) [7]. The glycine-to-nitrate molar ratio used
to fabricate BZCY powders is G/N = 1/2, because it can
fabricate nanosized and single-phase ceramic powders [7].
All synthesized powders were calcined at 1400 ◦C for
5 h in air. From our previous result [7], the calcined
Ba(Zr0.8−xCexY0.2)O2.9 ceramics (x = 0.0–0.8) have similar
particle sizes of ∼35–45 nm, indicating that the size effect in
Raman vibration could be ignored.
For in situ XRD measurements, a high-temperature
Rigaku model MultiFlex x-ray diffractometer with Cu Kα1
Figure 1. X-ray diffraction of BZCY (x = 0.0–0.8) taken at room
temperature. The dashed line is a guide for 2θ shifts.
(λ = 0.154 06 nm) and Cu Kα2 (λ = 0.154 44 nm) radiation
was used in the range of 20–900 ◦C upon heating by steps
in an argon-containing atmosphere. The calcined BZCY
powders were placed and smoothly pressed on the platinum
sample holder. A sum of Gaussian and Lorentzian equations
was used to fit XRD spectra for determinations of structures
and lattice parameters of the unit cell. For micro-Raman
scattering, a double-grating Jobin Yvon model U-1000
double-monochromator with 1800 grooves mm−1 gratings
and a nitrogen-cooled CCD as a detector were employed. A
Coherent model Innova 90 argon laser of wavelength λ =
514.5 nm was used as an excitation source and the Raman
spectra were collected at 150–1000 cm−1 from 20–900 ◦C by
steps.
3. Results and discussion
Figure 1 shows the XRD spectra of BZCYs (x = 0.0–0.8)
ceramic powders at room temperature. A second phase was
not observed in any of these compounds, indicating that the
optimal glycine-to-nitrate process and calcining condition can
produce single-phase powders. The main reflection peaks of
Ba(Zr0.8Y0.2)O2.9 (BZY82) include (110), (200), (210), (220)
and (310), and weak peaks occur for (100), (111) and (222).
Figure 2. The (110) XRD spectra of BZCY (x = 0.0–0.8) at room
temperature. Solid and dashed lines represent reflections from Kα1
and Kα2 radiation, respectively.
This suggests a simple cubic (sc) unit cell according to the
structure-factor calculation [20]. The cubic lattice parameter
was estimated from the (110) peak (2θ = 29.75◦) and is a =
4.2436 A˚ for BZY82 at room temperature. As indicated by the
dashed line, the XRD peak shifts towards lower 2θ degrees as
cerium content increases, because Ce4+ (RVI = 0.87 A˚) has a
larger ionic radius than Zr4+ (RVI = 0.72 A˚) [21].
Single-peak reflections appear in the XRD spectra
of lower-cerium compounds (x = 0.0–0.4), indicating a
cubic phase above room temperature. As cerium increases
(x = 0.5–0.8), the XRD spectra exhibit obvious multi-peak
reflections, especially at higher 2θ . To study the phase
transition development as a function of cerium composition
(x), the (110) XRD reflections of BZCY (x = 0.0–0.8)
powders taken at room temperature are enlarged in figure 2
with fitting profiles. Solid and dashed lines represent
reflections from Kα1 and Kα2 radiation, respectively. The
(110) reflection exhibits an obvious two-peak splitting (from
each radiation) for x= 0.5–0.8, especially a significant shift to
Figure 3. Micro-Raman spectra of BZCY (x = 0.0–0.8) taken at
room temperature. The dashed lines are guides for frequency shifts.
‘1–4’ and ‘#’ indicate four major modes and a shoulder vibration in
BCY82.
low 2θ angle in Ba(Zr0.2Ce0.6Y0.2)O2.9. A similar two-peak
splitting occurs in (210) and (220) reflections as seen in
figure 1 for x = 0.5–0.8. These two-peak splittings suggest a
rhombohedral phase, because two spacings are expected from
the (110), (210) and (220) reflections for a rhombohedral unit
cell according to the lattice equation;
1/d2 = [(h2 + k2 + l2)sin2α + 2(hk + kl+ hl)
× (cos2α − cosα)]/[a2R(1− 3cos2α + 2cos3α)] (1)
where (h, k, l) and (aR, α) are crystallographic orientation
and lattice parameters of the rhombohedral unit cell,
respectively [20]. In addition, the (200) reflection begins
to appear as a two-peak splitting in Ba(Zr0.2Ce0.6Y0.2)O2.9
as shown in figure 1, implying a development of a minor
monoclinic phase in the rhombohedral matrix. According to
equation (1), only a single XRD peak is allowed from the
(200) reflection for a rhombohedral (R) unit cell. The polar
axis of the monoclinic (M) phase is contained in the (110)
plane along a direction between that of the tetragonal and
rhombohedral polar axes. Additional XRD peaks can occur
in the (200) reflection for a monoclinic structure as observed
in the monoclinic PZT ceramic [22]. The sudden shift (to
low angle) in the (110) reflection of Ba(Zr0.2Ce0.6Y0.2)O2.9 is
likely associated with the appearance of a monoclinic phase.
These results suggest that a minor monoclinic phase coexists
in the rhombohedral matrix for higher-cerium BZCYs
ceramics (x = 0.5–0.8). This is consistent with the previous
Figure 4. In situ micro-Raman spectra of BZCY (x = 0.5–0.8)
upon heating. The dashed lines are guides for frequency shifts as
temperature increases.
neutron diffraction results, which suggested a coexistence of
rhombohedral and monoclinic phases for Ba(Ce0.8Y0.2)O2.9
(BCY82) at room temperature [19].
Figure 3 shows the micro-Raman spectra of BZCY (x =
0.0–0.8) ceramic powders at room temperature. The major
vibrations of Raman modes of BZY82 appear at ∼240,
∼370, ∼420, ∼500, ∼560 and ∼720 cm−1 as indicated by
arrows. As indicated by the dashed lines, vibration modes
shift towards lower frequency as cerium content increases,
due to the larger atomic mass of cerium compared with
Zr. As indicated by the ‘*’, a broad Raman mode as a
shoulder (beside the 360 cm−1 vibration) begins to develop
near 380 cm−1 in BZCY442 and its intensity grows stronger
as cerium increases. The relative intensities of Raman modes
near 350 and 380 cm−1 become dominant vibrations and
are stronger than the Raman mode near 680 cm−1 for
x = 0.5–0.8. The occurrence of an extra vibration mode
is consistent with the XRD result, in which an obvious
multi-peak splitting appears in the higher-cerium BZCY
ceramics (x = 0.5–0.8), due to the reduction in symmetry
from a cubic to a rhombohedral phase.
To explain the Raman modes of BCY82, a shoulder
vibration (‘#’) and four major modes (‘1–4’) are marked
in figure 3. Their frequencies are v# ∼= 305 cm−1,
v1 ∼= 332 cm−1, v2 ∼= 352 cm−1, v3 ∼= 440 cm−1 and
v4 ∼= 635 cm−1. The BaCeO3 rhombohedral R3¯c phase
(two formula units per primitive cell) has an irreducible
representation as [23]
0 = A1g(R)+ 4Eg(R)+ 3A2g(S)+ 2A1u(S)+ 3A2u(IR)
+ 5Eu(IR)+ A2u(A)+ Eu(A) (2)
where (R), (S), (IR) and (A) represent Raman-active, silent,
IR-active and acoustic modes, respectively. Three major Eg
modes were observed at 104, 322 and 344 cm−1 in the
R3¯c-phase BaCeO3, in which 322 and 344 cm−1 correspond
to the Ce–O stretching vibrations [23]. Y2O3 has three major
Raman-active vibrations near 302, 332 and 370 cm−1, which
correspond to the Y–O stretching modes [24]. Thus, the
Raman modes of v1 ∼= 332 cm−1 and v2 ∼= 352 cm−1 in
BCY82 can be attributed to the Ce–O and Y–O stretching
vibrations. The shoulder vibration of v# ∼= 305 cm−1 likely
correlates to the 302 cm−1 vibration of the Y–O stretching
modes [24]. Note that various inter-atomic distances between
Ce4+ and O2− ions can cause different force constants and
vibration frequencies. As shown in figure 3, v1 and v2 increase
with decreasing x as the heavier Ce4+ ions are replaced by
Zr4+ ions. The Raman modes of v1 and v2 merge into a single
mode for x = 0.0–0.3 due to the increase of symmetry from
the rhombohedral to the cubic phase. This result reveals that
the Raman modes associated with the X–O (X = Ce, Zr, Y)
stretching modes in the region of 330–380 cm−1 are sensitive
to the change of cerium content in the BZCY system.
The weak and broad Raman mode of v3 ∼= 440 cm−1 does
not occur in the R3¯c-phase BaCeO3. A single Raman vibration
of ∼461 cm−1 was observed in the fluorite structure CeO2
and corresponds to the F2g Raman-active triply degenerate
mode [25]. This mode is the symmetrically radial breathing
mode of the CeO8 vibration unit [26]. The Raman spectrum
of CeO2–ZrO2 ceramic also exhibits a strong vibration near
470 cm−1 due to the F2g mode of the fluorite-type lattice [27].
Thus, the weak Raman vibration of v3 ∼= 440 cm−1 in BCY82
can be viewed as a symmetric radial breathing mode of the
six oxygen ions around Ce4+ and Y3+ ions in the perovskite
structure, in which the frequency increases with decreasing x
as the heavier Ce4+ ions are replaced by Zr4+ ions.
Figure 5. Temperature-dependent Raman vibration (near
630–730 cm−1) and d spacing calculated from the (110) XRD
reflections of BZCY (x = 0.5–0.8) upon heating. The dashed lines
indicate the R–C transition temperatures.
A strong and broad Raman vibration appears in the region
of 620–650 cm−1 in Y2O3–ZrO2, CeO2–ZrO2 [28, 29] and
Zr1−xYxO2−x/2 [30]. The 640 cm−1 vibration in the 3% (mole
fraction) Y2O3–ZrO2 was attributed to the Zr–O stretching
mode with Zr4+ and O2− ions vibrate along the z axis in
the structure of tetragonal-phase ZrO2 [31]. Thus, the v4 ∼=
635 cm−1 of BCY82 in figure 3 should correspond to the
Ce–O stretching mode. The v4 shifts to higher frequency with
decreasing x as the heavier Ce4+ ions are replaced by Zr4+
ions.
To illustrate the evolution of Raman spectra as
temperature increases, in situ temperature-dependent micro-
Raman spectra are given in figure 4 for BZCY (x =
0.5–0.8) upon heating. As indicated by the dashed lines,
the Raman modes near 640–660 cm−1 shift to higher
frequencies as temperature increases. The double peaks near
340–370 cm−1 become broader and their relative intensities
decrease gradually as temperature increases.
Figure 5 shows temperature-dependent Raman vibrations
near 630–730 cm−1 and d spacings of BZCY ceramic
powders for the higher-cerium compounds (x = 0.5–0.8) upon
heating. The d spacing calculated from the (110) XRD peak
and 2θ reflection obey the Bragg law, 2dhkl sin θhkl = nλ.
Figure 6. Temperature-dependent lattice parameters calculated
from the (110) XRD reflections of BZCY (x = 0.5–0.8) upon
heating. The dashed lines indicate the R–C transition temperatures.
The Raman vibration mode (near 630–730 cm−1) exhibits a
step-up-like increase in frequency as temperature approaches
the structural transition, while two d spacings from the (110)
reflection merge into a single d spacing of the cubic phase.
For Ba(Zr0.3Ce0.5Y0.2)O2.9, the rhombohedral (R)–cubic
(C) transition takes place near 200 ◦C upon heating. This
transition shifts toward higher temperature as cerium content
increases, except for BCY82.
Figure 6 shows temperature-dependent lattice parameters
(a and α) of the rhombohedral and cubic phases of
higher-cerium BZCY (x = 0.5–0.8) upon heating. The lattice
parameters of the unit cell were determined by fitting the (110)
reflection, which is the most pronounced peak. The lattice
parameters exhibit a step-up-like anomaly as temperature
approaches the transition temperature as indicated by the
dashed line. The gradual increase of lattice parameters (aR and
aC) is mainly due to thermal expansion of the unit cell. Results
for lower-cerium BZCY (x = 0.0–0.4) ceramic powders are
not shown because they have no obvious phase transition
above room temperature.
The phase diagram (transition temperature versus Ce
content) of BZCY (x = 0.0–0.8) ceramics upon the heating
process is summarized in figure 7. A rhombohedral (R)–cubic
Figure 7. Phase diagram (transition temperature versus Ce content)
of calcined BZCY (x = 0.0–0.8) ceramic powders. The dashed line
is the estimated phase boundary. Rhombohedral (monoclinic)
represents a minor monoclinic phase coexists in the rhombohedral
matrix.
(C) phase transition occurs in higher-cerium BZCY ceramics
for x = 0.5–0.8. In addition, a minor monoclinic phase
coexists in the rhombohedral matrix for x = 0.5–0.8. The
R–C transition temperature increases with increasing Ce
content, except that the transition of BCY82 occurs at lower
temperature than Ba(Zr0.1Ce0.7Y0.2)O2.9. This may imply
that the R phase is favored both by Ce replacing Zr, and by
Ce–Zr disorder on the perovskite B sites.
4. Conclusions
In situ temperature-dependent micro-Raman scattering and
XRD have been used to investigate structures, lattice
parameters, Raman vibration modes and phase transitions
of calcined BZCY ceramics (x = 0.0–0.8) synthesized by
the glycine–nitrate combustion process with G/N = 1/2. A
second phase (other than perovskite) was not observed for
BZCY ceramic powders calcined at 1400 ◦C for 5 h. A
rhombohedral–cubic transition was observed in higher-cerium
BZCYs (x = 0.5–0.8) and the transition shifts towards higher
temperature as cerium content increases, except for BCY82. A
minor monoclinic phase coexists in the rhombohedral matrix
in the higher-cerium BZCYs (x = 0.5–0.8). The lower-cerium
BZCY ceramics (x = 0.0–0.4) have only a cubic phase at and
above room temperature. The X–O (X = Ce, Zr, Y) stretching
modes are sensitive to the change of cerium content and
can be used to study the doping or substitution effects of
the electrical conductivity and electrochemical properties in
proton-conducting BZCY ceramics. This work reveals that the
lower-cerium BZCY (x = 0.0–0.4) ceramics exhibit thermal
structural stability in the high-temperature region and are
promising for applications of proton-conducting solid oxide
fuel cells.
Acknowledgments
The authors would like to thank Dr J Liang (Fu Jen
Catholic University) for the Raman scattering apparatus.
This work was supported by the DOE under subcontract
DE-AC06-76RL01830 from Battelle Memorial Institute and
PNNL, and by the National Science Council of Taiwan grant
nos. 96-2112-M-030-001 and 100-2112-M-030-002-MY3.
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