A ferroelectric monoclinic phase of space group $Cm$ ($M_A$ type) has been
discovered in 0.65Pb(Mg$_{1/3}$Nb$_{2/3})O_3$-0.35PbTiO$_3$ by means of high
resolution synchrotron X-ray diffraction. It appears at room temperature in a
single crystal previously poled under an electric field of 43 kV/cm applied
along the pseudocubic [001] direction, in the region of the phase diagram
around the morphotropic phase boundary between the rhombohedral (R3m) and the
tetragonal (P4mm) phases. The monoclinic phase has lattice parameters a = 5.692
A, b = 5.679 A, c = 4.050 A and $\beta $ = $90.15^{\circ}$, with the b$_m$-axis
oriented along the pseudo-cubic [110] direction . It is similar to the
monoclinic phase observed in PbZr$_{1-x}$Ti$_x$O$_3$, but different from that
recently found in Pb(Zn$_{1/3}$Nb$_{2/3})O_3$-PbTiO$_3$, which is of space
group $Pm$ ($M_C$ type).Comment: Revised version after referees' comments. PDF file. 6 pages, 4
  figures embedde

B. Noheda

D. Cox

D. E. Cox

D. Vanderbilt

G. Shirane

G. Xu

J. Kuwata

K. Aizu

K. Harada

L. Bellaiche

L. E. Cross

M. Dong

O. Noblanc

S.-E. Park

T. Kobayashi

T. R. Shrout

Y. Lu

Z.-G. Ye

English

arXiv

A ferroelectric monoclinic phase of space group Cm (MA type) has been discovered in 0.65 Pb(Mg1/3Nb2/3)O3-0.35 PbTiO3 by means of high-resolution synchrotron x-ray diffraction. It appears at room temperature in a single crystal previously poled under an electric field of 43 kV/cm applied along the pseudocubic [001] direction, in the region of the phase diagram around the morphotropic phase boundary between the rhombohedral (R3m) and the tetragonal (P4mm) phases. The monoclinic phase has lattice parameters a=5.692 Å, b=5.679 Å, c=4.050 Å, and β=90.15°, with the bm axis oriented along the pseudocubic [110] direction. It is similar to the monoclinic phase observed in PbZr1-xTixO3, but different from that recently found in Pb(Zn1/3Nb2/3)O3-PbTiO3, which is of space group Pm (MC type)

Ye, Z.-G.

Noheda, B.

Dong, M.

Cox, D.

Shirane, G.

NARCIS 

Monoclinic phase in the relaxor-based piezoelectric/ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 system

A ferroelectric monoclinic phase of space group Cm (MA type) has been discovered in 0.65 Pb(Mg1/3Nb2/3)O3-0.35 PbTiO3 by means of high-resolution synchrotron x-ray diffraction. It appears at room temperature in a single crystal previously poled under an electric field of 43 kV/cm applied along the pseudocubic [001] direction, in the region of the phase diagram around the morphotropic phase boundary between the rhombohedral (R3m) and the tetragonal (P4mm) phases. The monoclinic phase has lattice parameters a=5.692 Å, b=5.679 Å, c=4.050 Å, and β=90.15°, with the bm axis oriented along the pseudocubic [110] direction. It is similar to the monoclinic phase observed in PbZr1-xTixO3, but different from that recently found in Pb(Zn1/3Nb2/3)O3-PbTiO3, which is of space group Pm (MC type).

Ye, Z.-G.,

Noheda, B.,

Dong, M.,

Cox, D.,

Shirane, G.,

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University of Groningen Research Database

  
 University of Groningen
Monoclinic phase in the relaxor-based piezoelectric/ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3
system
Ye, Z.-G.; Noheda, Beatriz; Dong, M.; Cox, D.; Shirane, G.
Published in:
Physical Review B
DOI:
10.1103/PhysRevB.64.184114
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Citation for published version (APA):
Ye, Z-G., Noheda, B., Dong, M., Cox, D., & Shirane, G. (2001). Monoclinic phase in the relaxor-based
piezoelectric/ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 system. Physical Review B, 64(18), [184114]. DOI:
10.1103/PhysRevB.64.184114
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Monoclinic phase in the relaxor-based piezoelectricÕferroelectric
PbMg1Õ3Nb2Õ3O3-PbTiO3 system
Z.-G. Ye,1 B. Noheda,2 M. Dong,1 D. Cox,2 and G. Shirane2
1Department of Chemistry, Simon Fraser University, Burnaby, BC, Canada V5A 1S6
2Physics Department, Brookhaven National Laboratory, Upton, New York 11973-500
~Received 12 June 2001; published 24 October 2001!
A ferroelectric monoclinic phase of space group Cm ~M A type! has been discovered in
0.65 Pb~Mg1/3Nb2/3!O3-0.35 PbTiO3 by means of high-resolution synchrotron x-ray diffraction. It appears at
room temperature in a single crystal previously poled under an electric field of 43 kV/cm applied along the
pseudocubic @001# direction, in the region of the phase diagram around the morphotropic phase boundary
between the rhombohedral (R3m) and the tetragonal (P4mm) phases. The monoclinic phase has lattice
parameters a55.692 Å, b55.679 Å, c54.050 Å, and b590.15°, with the bm axis oriented along the
pseudocubic @110# direction. It is similar to the monoclinic phase observed in PbZr12xTixO3, but different from
that recently found in Pb~Zn1/3Nb2/3!O3-PbTiO3, which is of space group Pm ~M C type!.
DOI: 10.1103/PhysRevB.64.184114 PACS number~s!: 77.84.Bw, 61.10.Nz
I. INTRODUCTION
The complex perovskite Pb~Mg1/3Nb2/3!O3 ~PMN! exhib-
its typical relaxor-type ferroelectric properties which have
been intensively studied for both fundamental and practical
reasons.1–3 The relaxor state is characterized by the frustra-
tion of local polarizations which prevents long-range ferro-
electric order from developing completely. Although the lo-
cal symmetry of the polar domains is rhombohedral, the
macroscopic symmetry of PMN remains cubic below the
temperature of maximum permittivity. A ferroelectric phase
can be induced either by application of an electric field along
@111#cub ,4 or by partial substitution of Ti41 for the complex
(Mg1/3Nb2/3)41 ions.5 In both cases, the micropolar domains
transform into macrodomains with cubic-to-rhombohedral
symmetry breaking.4,6 With Ti substitution, a complete solid
solution forms between PMN and PbTiO3, (12x)PMN
2xPT ~PMN-PT!, with a morphotropic phase boundary
~MPB! located at x’0.35, which has hitherto been believed
to represent the frontier between the rhombohedral ~relaxor
side! and tetragonal ~ferroelectric side! phases,5 as illustrated
in Fig. 1.
Single crystals of PMN-PT and other relaxor-PT solid so-
lutions, namely, Pb~Zn1/3Nb2/3!O3-PT ~PZN-PT!, with com-
positions near the respective MPB’s, have been reported to
exhibit very high piezoelectric coefficients (d33
.2500 pC/N), extremely large piezoelectric strains
~.1.7%!, and very high electromechanical coupling factors
(k33.92%).7–11 Such excellent properties point to a poten-
tial revolution in electromechanical transduction for a broad
range of applications. From the crystal chemistry viewpoint,
the strong piezoelectric response of those materials is asso-
ciated with the MPB, and very recently intensive theoretical
and experimental research has been undertaken in order to
understand the origin of these enhanced piezoelectric prop-
erties. The experimental breakthroughs have been achieved
by the discovery of ferroelectric monoclinic and orthorhom-
bic phases by high-resolution synchrotron x-ray diffraction.
In PbZr0.52Ti0.48O3 ~PZT48!, a monoclinic phase with space
group Cm ~of M A type, in the Vanderbilt and Cohen
notation12! was found below room temperature. In such a
phase, the monoclinic b axis lies along pseudocubic @11¯0# ,
and the polarization is in the (11¯0) plane.13,14 In the PZN-PT
system, an orthorhombic phase was found to exist between
the rhombohedral and tetragonal phases at around 10%PT.15
Upon application of an electric field along @001#cub , evi-
dence of polarization rotation via a monoclinic phase has
been shown for PZN-8%PT,16 which is in agreement with the
theoretical considerations by first-principles calculations for
the PZT case.17,18
So far, several pictures of the phase states near the MPB
of the PMN-PT system have been proposed. Shrout et al.5
initially suggested that the rhombohedral R3m phase of
smaller Ti concentration and the tetragonal P4mm phase of
higher Ti content, were separated by a fairly sharp phase
boundary at 35%PT. The authors of Ref. 19 reported a large
composition range around the MPB in which the rhombohe-
dral and tetragonal phases coexist. Optical domain studies
showed that the R3m and P4mm phases may coexist at
room temperature, with transformation from the R3m into
the P4mm phase taking place over a wide temperature
interval.6 In the present paper, we report the results of a
high-resolution synchrotron x-ray diffraction study of
0.65 Pb~Mg1/3Nb2/3!O3-0.35 PbTiO3 (PMN-35%PT) single
FIG. 1. Phase diagram of the PMN-PT solid solution system.
Solid circles and related phase boundaries are adapted from Ref. 5.
C, R, and T refer to cubic, rhombohedral, and tetragonal regions,
respectively. The diagonally shaded area represents the monoclinic
M phase region, updated based on the present work.
PHYSICAL REVIEW B, VOLUME 64, 184114
0163-1829/2001/64~18!/184114~5!/$20.00 ©2001 The American Physical Society64 184114-1
crystals, showing unambiguous evidence of a monoclinic
phase, which is stable between the rhombohedral and tetrag-
onal phases near the MPB.
II. EXPERIMENT
Single crystals of PMN-35%PT were grown from a high-
temperature solution using an optimum flux composition
(50 wt %PMNT149 wt %PbO11 wt %B2O3).20 Two plate-
lets, No. 1, 65 mm thick, and No. 2, 165 mm thick, were cut
parallel to the reference (001)cub plane, and polished with
fine diamond paste ~down to 1 mm!. The (001)cub faces were
covered with Ag paste, Au wires were attached, and platelets
Nos. 1 and 2 were poled under electric fields of 43 and 5
kV/cm, respectively, which were applied along @001#cub at
200 °C ~above TC! and maintained while cooling down to
room temperature. The samples were then short circuited for
30 min before the electrodes were removed. Synchrotron
x-ray diffraction experiments were performed at the
Brookhaven National Synchrotron Light Source ~NSLS!.
The PMN-35% PT crystal No. 1 poled at 43 kV/cm was
studied at beam line X22A with 30-keV x-rays from the
third-order reflection of a Si~111! monochromator. The mea-
surements were made on a Huber four-circle diffractometer
equipped with a Si~111! analyzer. X-ray powder diffraction
was also performed on PMN-35%PT at beam line X7A with
18-keV x-rays from a Si~111! double-crystal monochromator
(l’0.7 Å.) PMN-PT crystal No. 2, previously poled at 5
kV/cm was crushed and sieved to produce a powder sample
with large crystallites ~38–44 mm! that we call a properly
arranged single crystal ~PASC!, in order to obtain sharp pow-
der lines free from sample-broadening effects. A 0.2-mm
capillary loaded with the specimen was mounted on a Huber
diffractometer equipped with a Ge~220! analyzer. The result-
ing instrumental resolution is about 0.005° on the 2u scale.
III. RESULTS AND DISCUSSION
Figure 2 gives three examples of the contour maps ob-
served in different cubic zones around the ~002!, ~300!, and
~330! reflection peaks for the PMN-35%PT crystal No. 1.
For these experiments, the Bragg indices H5K5L51 were
defined to correspond to the cubic lattice parameters a5b
5c54.016 Å for all the cases.
To interpret the diffraction patterns observed in Fig. 2 and
to illustrate the structure of the PMN-35%PT, we need to
consider the possible domain configurations based on group-
subgroup symmetry relationship. The high-temperature pro-
totype phase has Pm3¯m space group symmetry. The phase
transitions into a rhombohedral R3m phase, or a monoclinic
m phase would normally result in eight or 24 ~fully! ferro-
electric or ~partially! ferroelastic domain states,
respectively.21 The domain structures are therefore very com-
plicated, especially for the monoclinic phase. However, a
much-simplified situation is produced by electric-field pol-
ing, which constrains the c axis to lie along the pseudocubic
@001# direction, analogous to the situation previously dis-
cussed for PZN-8%PT.16 The monoclinic domain configura-
tion now consists of two b domains related by a 90° rotation
around the c axis, each of which contains two domains.
The contour map of Fig. 2~a! shows a single d spacing in
the H0L zone measured around the ~002! reflection, which
gives the parameter c54.050 Å. The fact that a single d
spacing was observed in this region demonstrates that the c
axis is indeed fixed along the poling field direction of
pseudocubic @001#, and that the poled state remains stable
after the field is removed. The very weak extra peaks ob-
served in the transverse direction may correspond to slightly
misaligned regions close to the surface, since they were not
observed with high-energy x-rays at 67 keV. Figure 2~b! is
the contour map obtained around the pseudocubic ~300! peak
in the H0L zone, and shows a symmetrical splitting along
the transverse L direction. This splitting can be attributed to
the two a domains, but it is in sharp contrast to the three
peaks observed for the ~200! reflection from PZN-8%PT,15
which has monoclinic symmetry of type M C ~in the
Vanderbilt-Cohen notation12!. On the other hand, the contour
map around the pseudocubic ~330! reflection shown in Fig.
2~c! is seen to contain three peaks, and in conjunction with
Fig. 2~b! provides the signature of a monoclinic structure of
M A type with am and bm directed along pseudocubic @1¯ 1¯ 0#
and @11¯0# . The split peak is located at H5K52.993 and the
single peak at H5K53.000, corresponding to lattice param-
eters am55.692 Å and bm55.679 Å. The transverse separa-
FIG. 2. Contour maps observed around ~002!, ~300!, and ~330!
reflection peaks in the cubic H0L ~a!, H0L ~b!, and HHL ~c! zones,
respectively, for a poled PMN-35%PT crystal. H5K5L51 has
been defined to correspond to d54.016 Å for all the cases.
Z.-G. YE, B. NOHEDA, M. DONG, D. COX, AND G. SHIRANE PHYSICAL REVIEW B 64 184114
184114-2
tion of the split peaks is L50.022, yielding a monoclinic
angle b590.15°. The projection of the monoclinic angle
(b8’b&) can also be deduced independently from the
splitting of the ~300! peak in Fig. 2~b!, namely, L50.012,
which yields a similar value of 90.16°. Finally, we note that
although a rhombohedral domain structure could also give
qualitatively similar features, such a structure can immedi-
ately be excluded, since the requirements of rhombohedral
symmetry would impose constraints on the lattice parameters
@e.g., cm
2 5(am2 1bm2 )/4# which are clearly not satisfied. Thus
we conclude that a monoclinic phase of M A type has been
unambiguously shown to exist in the PMN-35%PT crystal.
Figure 3 shows longitudinal and transverse linear scans for
each of the ~002!, ~300!, and ~330! reflections in Fig. 2. The
lines are fits to Gaussian profiles. These scans confirm the
monoclinic symmetry and lattice parameters deduced above.
We have also studied the weakly poled (E,5 kV/cm)
PMN-35%PT crystal ~No. 2! in the form of crushed ~PASC!
powders by x-ray powder diffraction at X7A. Figure 4 shows
the sharp powder lines from a PASC sample with a grain size
between 38 and 44 mm. Only a single peak was observed for
the (100)cub reflection, while both (110)cub and (111)cub re-
FIG. 3. Longitudinal and
transverse linear scans for each of
the ~002!, ~300!, and ~330! reflec-
tions in Fig. 2. The lines are fits to
Gaussian profiles.
MONOCLINIC PHASE IN THE RELAXOR-BASED . . . PHYSICAL REVIEW B 64 184114
184114-3
flections showed split doublets. These patterns can be clearly
indexed as a single rhombohedral R phase with a54.023 Å
and a589.88°. Therefore, unpoled or weakly poled PMN-
35%PT samples show an average rhombohedral phase, con-
sistent with the reported MPB phase diagram.5
IV. CONCLUSIONS
A monoclinic phase of space group Cm ~M A type! was
discovered in a PMN-35%PT crystal at room temperature by
means of high-resolution synchrotron x-ray diffraction. This
M A phase has its monoclinic am and bm axes oriented along
the pseudocubic @11¯0# and @110# directions, respectively,
with the cm axis along the pseudocubic @001# direction. The
unit-cell parameters are found to be am(’ac&)55.692 Å,
bm(’ac&)55.679 Å, cm(’ac)54.050 Å, and b590.15°.
This monoclinic phase exhibits the same crystallographic
features as the one reported for PbZr12xTixO3 ~i.e., a doubled
cell rotated by 45° around the c axis with respect to the
tetragonal unit cell!,13 but is different from the M C-type
monoclinic phase ~space group Pm! recently reported in
PZN-8%PT, where the monoclinic bm axis lies along
@01¯0#cub .15
The monoclinic phase appears at room temperature in a
PMN-35%PT crystal previously poled under an electric field
of 43 kV/cm applied along the @001#cub direction. On the
other hand, unpoled and weakly poled PMN-35%PT samples
exhibit an average rhombohedral symmetry. Although poling
at high field along the @001#cub direction may be necessary in
order to produce a long-range monoclinic phase for the com-
position, this point is not yet fully settled, and we hope to
clarify it in future experiments. The existence of the mono-
clinic phase in PMN-35%PT allows us to construct an up-
dated phase diagram for the PMN-PT solid solution system,
in which a narrow monoclinic phase region exists between
the rhomboheral R3m and tetragonal P4mm phases at low
temperatures, as indicated by the dashed area in Fig. 1. More
extended work is underway in order to provide a better un-
derstanding of the nature of the MPB and the origin of the
outstanding piezoelectric performance of PMN-PT crystals,
and will be reported elsewhere.
After the submission of this paper, two important papers
have appeared: Xu et al.22 reported the observation of mono-
clinic domains by polarized light microscopy, and Lu et al.23
showed the existence of an orthorhombic phase in 0.67PMN-
0.33PT crystals.
ACKNOWLEDGMENTS
This work was supported by ONR Grant No. N00014-99-
1-0738 and by the U.S. DOE under Contract No. DE-AC02-
98CH10886. We thank John Hill, Ben Ocko, and Zhong
Zhong for very useful discussions.
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Z.-G. YE, B. NOHEDA, M. DONG, D. COX, AND G. SHIRANE PHYSICAL REVIEW B 64 184114
184114-4
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Crossref

Monoclinic phase in the relaxor-based piezoelectric/ferroelectric
                    
                      
                        
                          
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