Raman spectra and structural stability in B-
site manganese doped 
(Bi0.5Na0.5)0.925Ba0.075TiO3 relaxor 
ferroelectric ceramics
Authors: J. Anthoniappen, C.S. Tu, P.-Y. Chen, C.-S. 
Chen, Y.U. Idzerda, and S.-J. Chiu
NOTICE: this is the author’s version of a work that was accepted for publication in Journal of the 
European Ceramic Society. Changes resulting from the publishing process, such as peer 
review, editing, corrections, structural formatting, and other quality control mechanisms may not 
be reflected in this document. Changes may have been made to this work since it was submitted 
for publication. A definitive version was subsequently published in Journal of the European 
Ceramic Society, [VOL# 35, ISSUE# 13, (November 2015)] 
DOI# 10.1016/j.jeurceramsoc.2015.05.002
Anthoniappen, J., C. S. Tu, P. Y Chen, Y. U. Idzerda, and S. J. Chiu. "Raman spectra and 
structural stability in B-site manganese doped (Bi0.5Na0.5)0.925Ba0.075TiO3 relaxor 
ferroelectric ceramics." Journal of the European Ceramic Society 35, no. 13 (November 2015): 
3495-3506. https://dx.doi.org/10.1016/j.jeurceramsoc.2015.05.002.
Made available through Montana State University’s ScholarWorks 
scholarworks.montana.edu 
Raman spectra and structural stability in B-site 
manganese doped (Bi0.5Na0.5)0.925Ba0.075TiO3 
relaxor ferroelectric ceramics
J. Anthoniappen a,g,∗, C.S. Tu b, P.-Y. Chen c, C.-S. Ch
a Graduate Institute of Applied Science and Engineering, Fu Jen Catholic University, New
b Department of Physics, Fu Jen Catholic University, New Taipei City 24205, Taiwan
c Department of Mechanical Engineering, Ming Chi University of Technology, New Taipe
d Department of Mechanical Engineering, Hwa Hsia University of Technology, New Taip
e Dep
f Nat
g Dep
Abstrac
Soft X-ray a ama
been studie 0.075T
High-resolu f rho
structures i ped 
spectra of 0 o tetr
anomaly, while 0.2–2% Mn-doped BN7.5BT show softening behavior near 290 ◦C upon heating. Raman spectra and 
synchrotron XRD indicate that Mn doping can enhance structural thermal stability in BN7.5BT ceramics.
1. Introdu
Lead-fre
based mate
their prom
ties, which
piezoceram
between a 
(abbreviate
due to the 
between rh
x = 0.06–0
erties in M
enhanced, 
ature Tc sigction
e bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT)
rials have attracted so much attention because of 
ising piezoelectric and electromechanical proper-
 are comparable to lead based Pb(Zr,Ti)O3 (PZT) 
ics [1]. Among the studied materials, solid solutions 
rhombohedral (BNT) and tetragonal BaTiO3(BT)
d as BN100xBT) have been of particular interest 
existence of morphotropic phase boundary (MPB) 
ombohedral (R) and tetragonal (T) structures near
.08 [2–5]. Though piezoelectric and dielectric prop-
PB compositions of BN100xBT are remarkably 
the depolarization temperature Td and Curie temper-
nificantly were reduced at the MPB. In contrast to 
Several studies have been reported on effects of manganese 
doping on lead based and lead-free solid solutions. It was 
found that Mn substitution could be effective in inducing hard 
characteristics in (1 − y)Pb(Zn1/3Nb2/3)O3–yPbTiO3 (PZNT) 
single crystals [8,9]. Luo et al. [10] showed incre-ments of 
coercive field, Curie temperature, and stability of the 
ferroelectric rhombohedral phase in 3 at% Mn-doped 
0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (PMNT) single crystals.
PZT the MPB in BN100xBT is strongly curved, thus leading 
to low-temperature stability [6]. For applications, the 
properties of BN100xBT ceramics need to be further 
improved. It has been reported that optimizing processing and 
modifying are major ways to improve piezoelectric properties 
[7].artment of Physics, Montana State University, Bozeman, MT 59717, USA
ional Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
artment of Physics, University of San Carlos, Cebu City 6000, Philippines
t
bsorption (XAS), transmission electron spectroscopy (TEM), R
d in B-site 0–2 mol% manganese (Mn) doped (Bi0.5Na0.5)0.925Ba
tion synchrotron XRD and TEM reveal two phase coexistence o
n 0 and 0.2%, and an orthorhombic structure in 1 and 2%Mn-do
% Mn reveal structural transition from two phase coexistence ten d, Y.U. Idzerda e, S.-J. Chiu f
 Taipei City 24205, Taiwan 
i City 24301, Taiwan
ei City 23567, Taiwan
n spectroscopy, and synchrotron XRD have 
iO3 (BN7.5BT) relaxor ferroelectric ceramics. 
mbohedral R3c and tetragonal P4bm 
BN7.5BT at room temperature. Raman 
agonal phase near 190 ◦C with a softening 
Fig. 1. Mn L-
ture. The soli
a set of standa
the Mn2+ and
figure legend,
Yan et al. [1
of 0.8P
ceramics in
on the Zn
[12] condu
Pb(Zn1/3N
indicated lo
Qm. In man
wall motio
reduction o
Zhang e
single crys
properties s
tromechani
be 483 pC
discovered
macroscop
tion tempe
to the und
substitution
tortion of
lead-free p
permittivity
order array
system du
[15].
Yao et
ing, and la
using brigh
tron diffrac
with Mn s
ing and in-
modulation
elastic stre
in the num
size of ab
along {110
ynchrotron XRD spectra in the range of 20–70◦ at room temperature.
ts are corresponding (1 1 1) and (2 0 0) diffraction patterns and cross-
SEM micrographs.
that the tetragonal domain states could be stabilized
ling along [0 0 1] direction and the piezoelectric coef-
d33 could reach 570 pC/N [17]. Recently we have
d that 0.5 mol% Mn doping in (Bi0.5Na0.5)1-xBaxTiO3
and 0.075) solid solutions can increase structural ther-
tability, depolarization temperature (Td), piezoelectricedge XAS signals in BN7.5BT–4% Mn sample at room tempera-
d black line is the experimental data. Red, blue and pink lines are
rds for various Mn valences. The green dashed line is the sum of
Mn3+ spectra. (For interpretation of the references to color in this
the reader is referred to the web version of this article.)
1] proposed that Mn3+ substitution on Ti and Zr sites
b(Zr0.52Ti0.48)O3–0.2Pb(Zn1/3Nb2/3)O3(PZT–PZN)
duces hardening effect, whereas Mn2+ substitution
-site stabilizes the perovskite phase. Priya et al.
cted Mn-doping on the PZT modified by 20 mol%
b2/3)O3 (PZN) relaxor material, and their studies
w dielectric loss and high mechanical quality factor
ganese oxide doped hard PZT compositions, domain
n could be pinned by the oxygen vacancy resulting in
f dielectric loss as well as enhancement of Qm [12].
t al. [13] reported that Mn doping in BN100xBT
tal could enhance ferroelectric and piezoelectric
ignificantly. The piezoelectric constant d33 and elec-
cal coupling coefficients (kt and k31) were found to
/N, 0.56, and 0.40, respectively. Sapper et al. [14]
that Mn-doped BN100xBT piezoceramics stabilize
ic polarization and consequently shift depolariza-
rature (Td) to higher temperatures as compared
oped BN100xBT. It was found that the suitable
Fig. 2. S
The inse
section
shown
by po
ficient
reporte
(x = 0
mal sof Mn ion into the B site induces the lattice dis-
perovskite MnO-doped (Na0.5Bi0.5)0.92Ba0.08TiO3
iezoceramics [15]. Temperature-dependent dielectric
indicates that the MnO addition reconstructs the dis-
destroyed by joining BaTiO3 in the Bi0.5Na0.5TiO3
e to the sizable radius of the B-site cations
al. [16] studied domain structure, octahedral tilt-
ttice structure of Mn:NBT—5.5%BT single crystals
t field and lattice imaging, and selected area elec-
tion (SAED). They reported the following results
ubstitution: (i) increased tendencies of FE order-
plane octahedral tilting; (ii) formation of structural
across domain boundaries, which may help relax
ss between FE domains; and (iii) an increase
ber of in-phase oxygen tilted regions, with a
out 2–8 nm and with a tendency of alignment
}. The Mn-doped NBT-6%BT single crystals have
coefficient
[18].
Therma
there is ve
induced by
troscopy ha
the structur
ics [19,20]
doping in B
micro-Ram
(XRD) as f
centrations
doping can
2. Experim
(Bi0.5Na
(Ti1−xMnx(d33), and electromechanical coupling factor (kt)
l phase stability is essential for applications. So far,
ry little understanding about the structural stability
Mn-doping in BNBT solid solutions. Raman spec-
s been used as an effective technique to investigate
al evolution in perovskite-type solid solution ceram-
. In this work, we have studied the effects of MnO2
N7.5BT [(Bi0.5Na0.5)0.925Ba0.075(Ti1−xMnx)O3] via
an spectroscopy and synchrotron X-ray diffraction
unctions of temperature for a sequence of Mn con-
(x= 0–2% Mn). Our results confirm that the MnO2
enhance structural phase thermal stability.
ental procedure
0.5)TiO3 (BNT) and (Bi0.5Na0.5)0.925Ba0.075
)O3 (BN7.5BT–xMn) (x= 0, 0.2, 1.0, and 2.0 mol%)
Fig. 3. Select b) [1 1
[1 1 1] zone a
ceramics w
purity (>9
and MnO2
amounts o
ethanol. Th
PM100 pla
The calcin
disks for
BNT and
Table 1
Raman vibrat
Phonon mode
Mode frequen
130
164*
192*
244
287
335
412*
480
521
577
720
780
852ed area diffraction patterns (SADP) of 0.2% Mn viewed along (a) [1 1 0] and (
xis. Arrows labeled in the SADPs indicate superlattice reflections.ere prepared by using solid state reaction. High
9%) powders of Bi2O3, Na2CO3, BaCO3, TiO2,
were used as starting materials. Stoichiometric
f powders were ball-milled for more than 24 h in
e mixture was calcined at 900 ◦C (2 h) and a Retsch
netary ball mill was used to reduce particle size.
ed powders were then pressed into 1.0 cm-diameter
sintering at 1150 ◦C (2 h) and 1170 ◦C (2 h) for
BN7.5BT-xMn, respectively. All polished sintered
samples we
stress.
Raman
ment (Nano
λ = 532 nm
A high ma
focus the la
Raman sca
ing from 25
ion frequencies (ω) and their mode assignments of (Bi0.5Na0.5)TiO3 (BNT) and BaT
assignment in polycrystalline Bi0.5Na0.5TiO3 at −110 ◦C Phonon
cy ω (cm−1) Mode assignment References Mode fr
A1(1) [24–26] 112
E(1) 181
E(2) 263
E(3) [27] 306
A1(2) [25,26,28] 485
A1(3) [27] 527
E(4) 531
E(5) [26,27,29] 716
A1(4) [26,27,29]
E(6) [26,27,29]
E(7) [27]
E(8) [27]
E(9) [27]1] zone axis. SADPs of 2% Mn viewed along (c) [0 1 0] and (d)re annealed at 600 ◦C for 30 min to remove residual
spectra were measured using a micro-Raman instru-
base, XperRam 200) equipped with a green laser of
and a TE-cooled CCD detector (1024 × 128 pixel).
gnification objective (40×, 0.75 NA) was used to
ser to a spot of ∼1m. For temperature-dependent
ttering measurements, the data were taken upon heat-
◦C to 290 ◦C. The high-resolution synchrotron XRD
iO3 (BTO) ceramics.
mode assignment in polycrystalline BaTiO3 at 25 ◦C
equency ω (cm−1) Mode assignment References
E(1) [36]
E(2) [33–36]
A1(1) [33,34]
B1 [33,34,36]
E(3) [34,35]
A1(2) [33,34,36]
E(4) [35,38]
A1(3) [33–35]
Fig. 4. (a) Ra
in the range o
perature with
Correspondin
dominant mo
was perfor
energy of 8
were fitted
and Loren
using a s
S-3400N
microscopy
JEOL JEM
X-ray abso
in total ele
6.3.1.1 of
tory. Absor
with linear
3. Results
Fig. 1 s
spectra (XA
ics. We bel
our compo
normalized
is calibrate
ence powd
spectra. Thman spectra of rhombohedral Bi1/2Na1/2TiO3 (BNT) at −110 ◦C
f 60–950 cm−1. Corresponding inset is the spectra at room tem-
dominant modes. (b) Raman spectra of BaTiO3 (BTO) at 25 ◦C.
g inset is the spectra in the orthorhombic phase (at −50 ◦C) with
des.
med at NSRRC (BL17B1) in Taiwan with a photon
keV (λ = 1.555 A˚). Both Raman and XRD spectra
by using PeakFit software with the sum of Gaussian
tzian profiles. Grain morphologies were obtained
canning electron microscope (SEM; HITACHI
FE-SEM). High-resolution transmission electron
(TEM) observations were carried out using the
-2100 LaB6. To determine oxidation states, the soft
rption spectra (XAS) of Mn L23-edge were recorded
ctron yield via sample current mode at beamline
Advanced Light Source Berkeley National Labora-
ption measurements were made at room temperature
photon polarization and normal incidence.
and discussion
hows the normalized Mn L-edge X-ray absorption
S) measured from 4% Mn-doped BN7.5BT ceram-
ieve that 4 mol% Mn is within the limit to represent
sitions studied in this work. The spectra have been
to the integrated peak area (L2 + L3) and energy
d by comparing the peak position of Mn3O4 refer-
er that is simultaneously collected with each sample
e 2nd peak energy of the reference powder is set to
Fig. 5. Temp
(c) 1% Mn, an
640.05 eV.
number of
The bindin
is indicated
fit from a l
(∼40% of t
the average
librium of
in the sinte
lent Mn4+
Rothery ru
solvent ion
tion [11]. I
Ti4+ (0.605
(1.38 A˚) io
than Ti4+, b
respectivel
replacing T
distribute a
The den
method, an
for 0.0, 0.2
retical denserature evolution of Raman spectra of (a) 0% Mn, (b) 0.2% Mn,
d (d) 2% Mn.
All reference powder samples are normalized by the
d-holes, resulting in absorption spectra per d-hole.
g energy at the absorption edge for each standard Mn
by arrow marks. The measured spectra can be well
inear combination of two reference powder spectra
he Mn2+ and ∼60% of Mn3+), to give an indication of
Mn valence. This result indicates an effective equi-
divalent Mn2+ (∼40%) and trivalent Mn3+ (∼60%)
red sample, although manganese presents as tetrava-
in the dopant oxide MnO2. According to the Hume
le, the difference in ionic size between solute and
s should be less than 15% to form a stable solid solu-
onic radius of Mn3+ (0.645 A˚) is similar to that of
A˚) and much smaller than Bi3+ (1.03 A˚) and Ba2+
ns. Ionic radius of Mn2+ (0.83 A˚) is 22.5% larger
ut is 20% and 55% smaller than Bi3+ and Ba2+ ions,
y. Therefore, it is likely that Mn3+ ions occupy B-site
i4+ causing oxygen vacancies, and Mn2+ ions may
t grain boundaries.
sity of the samples were measured by Archimedes
d are respectively ∼5.70, 5.75, 5.83 and 5.87 g/cm3
, 1.0, and 2% Mn, which are above 96% of the theo-
ity. Fig. 2 shows synchrotron XRD patterns taken at
Fig. 6. F
Table 2
Frequencies o
Composition
0%Mn
0.2%Mn
1%Mn
2%Mnits of Raman vibrational bands for 0% Mn, 0.2% Mn, 1% Mn, and 2% Mn at 25 ◦C
f dominant Raman modes at room temperature in 0–2% Mn-doped BN7.5BT ceram
A O band (cm−1) B O band (cm−1)
102 258 310
103 250 308
103 237 307
104 232 305and 290 ◦C. Dominant modes are labeled with arrow marks.
ics.
BO6 octahedra (cm−1)
525 615
520 611
513 597
505 594
ant Ra
room temp
grain morp
etching at 1
and the ave
1.0, and 2%
of (1 1 1) a
marked wit
phase coex
three (2 0 0
show ortho
peaks and o
As show
confirmed
high-resolu
in 0% Mn-d
[5]. Fig. 3(a
along [1 1 0
axis anti-ph
1/2{o o e}
which is the
three-axis
confirms tw
and d) do
Mn, thus r
tetragonal
the directio
(Fig. 3c) is
diffractions
es f
ortFig. 7. Temperature evolution of domin
erature. The insets (on the left side) show the SEM
hologies of the cross-section, obtained after thermal
distanc
gest an000 ◦C for 3 min. The grain size increases with MnO2
rage grain sizes are 2.1, 2.6, 4.6, and 5.2m for 0, 0.2,
Mn, respectively. The insets are diffraction patterns
nd (2 0 0) reflections at room temperature with peaks
h numbers and arrows. The 0 and 0.2% Mn show two
istence (rhombohedral and tetragonal) evidenced by
) peaks and two (1 1 1) peaks. Whereas, 1 and 2% Mn
rhombic structure evidenced by three distinct (2 0 0)
ne sharp (1 1 1) peak.
n in Fig. 3, the as-identified structures are further
by selected area diffraction patterns (SADP) from
tion TEM for 0.2 and 2% Mn. The phase coexistence
oped BN7.5BT has been shown in our previous work
) reveals the 1/2{o o o} superlattice diffraction spots
] zone axis, which belong to R3c phase with single-
ase a−a−a− octahedral tilting. Fig. 3(b) shows the
superlattice diffraction spots along [1 1 1] zone axis,
characteristic of the tetragonalP4bm symmetry with
equivalent in-phase ao ao c+ octahedral tilting. This
o phase coexistence (R + T) in 0.2% Mn. Fig. 3(c
not show any superlattice diffraction pattern in 2%
uling out the possibilities of rhombohedral R3c and
P4bm symmetries. However, one can observe that
n of both {1 0 0} diffractions in [0 1 0]-zoned SADP
orthogonal to each other, and three sets of {1 1 0}
in the [1 1 1]-zoned SADP (Fig. 3d) have different
room temp
Before g
compositio
(Bi0.5Na0.5
BNT is a w
rial at amb
(C3v6) [21,
group theo
for rhombo
E mode co
Raman sile
of 13 Rama
shows a tet
at 698 K, d
on the nucl
in the spac
and E mod
Fig. 4(a
−110 ◦C w
The sampl
−150 ◦C a
steps upon
modes at 2
except that
due to less
tion frequeman modes.
rom the transmission spots. These TEM results sug-
horhombic structure in 2% Mn-doped BN7.5BT at
erature.
oing into Raman spectra of Mn-doped BN100xBT
ns, the Raman spectra of both end compositions
)TiO3 (BNT) and BaTiO3 (BTO) were analyzed.
ell-known classic rhombohedral ferroelectric mate-
ient temperature and belongs to the space group R3c
22], containing two formula units (Z= 2) [23]. The
ry leads to 5A1, 5A2, and 10E vibrational modes
hedral BNT. One A1 and one doubly degenerate
rrespond to acoustic phonons, and 5A2 modes are
nt modes. Therefore, the irreducible representation
n and IR active modes is BNT = 4A1 + 9E [24]. BNT
ragonal P4bm (C4v2) structure (formula units, Z = 2)
etermined by neutron powder diffraction [25]. Based
ear site group analysis, the main Raman active modes
e group P4bm structure (Z= 2) include A1, B1, B2,
es [19].
) shows the deconvoluted spectrum of BNT at
ith 13 Raman modes in the range of 60–950 cm−1.
es were cooled down from room temperature to
nd then the spectra were obtained from −110 ◦C by
heating. The inset shows the spectrum of dominant
5 ◦C, which is similar to that measured at −110 ◦C,
the Raman bands at −110 ◦C are relatively sharper
phonon interaction. A compilation of Raman vibra-
ncies and their modes in rhombohedral (R3c) BNT are
given in Ta
works [24,2
have been i
of 100−20
tions. Band
associated
287 cm−1 m
is sensitive
bands are d
ments [31]
been assign
Fig. 4(b
at 25 ◦C. BFig. 8. Variation of full width at half maxima (FWHM) of
ble 1. In addition to Raman modes found in previous
6–30], Raman vibrations of 164, 192, and 412 cm−1
dentified as labeled by “*”. Bands located in the range
0 cm−1 are assigned to Na/Bi O stretching vibra-
s located in the range of 200–600 cm−1 are mainly
with Ti O stretching vibrations. In particular, the
ode involves only O Ti O bending motion, which
to the phase transition [26]. High-frequency Raman
ominated by vibrations involving oxygen displace-
. The high frequency modes (600–850 cm−1) have
ed to vibrations of the TiO6 oxygen octahedral [24].
) shows the deconvoluted phonon spectra of BTO
TO exhibits four different phases upon heating:
a rhomboh
Amm2 pha
6 to130 ◦C
The Raman
(Z = 1) can
Raman, BTO
metric mot
to the highe
that major R
ture (Z = 2)
previous st
and tetrago
the appearadominant Raman modes.
edral R3m phase below −90 ◦C, an orthorhombic
se at −90 to 6 ◦C, a tetragonal P4mm phase at
, and a cubic phase Pm¯3m above 130 ◦C [32,33].
active modes in the tetragonal P4mm space group
be represented by the irreducible representation;
= 3A1 + B1 + 4E [32]. The B1 mode indicates asym-
ion of the TiO6 octahedral and the A1(3) is related
st-wavenumber longitudinal optical mode [34]. Note
aman modes of BNT in the space group P4bm struc-
also have A1, B1, and E modes [25]. Based on the
udies [35,36], the Raman spectra of orthorhombic
nal phases in BTO are similar. The only difference is
nce of ortho vibration at 192 cm−1 in orthorhombic
reflec
phase as i
The subscr
E(3) mode
bohedral p
[39,40], an
are of tetra
Fig. 5 sh
25 to 290 ◦
bands are re
typical feat
shown in F
of 50–700 c
A1(4), and
deconvolut
pure BNT
an obvious
reveals an
degree of d
ium (mBa =
(mNa = 22.9
ference is t
310 cm−1.
tic vibratio
evidence fo
Fig. 6(e–h)
5 dominan
labeled asFig. 9. Synchrotron XRD spectra of (2 0 0) Bragg’sndicated by green arrow in the inset of Fig. 4(b).
ipt “ortho” signifies the orthorhombic phase. In brief,
is characteristic vibration of low-temperature rhom-
hase [35–38], ortho mode is of orthorhombic phase
d E(1), E(2), A1(1), B1, A1(2), E(4), and A1(3) modes
gonal P4mm phase [34,36].
ows the temperature-dependent Raman spectra from
C for 0, 0.2, 1, and 2% Mn-doped BN7.5BT. All
latively broad, indicating band overlapping, which is
ure for perovskite relaxor ferroelectric materials. As
ig. 6(a–d) for 0 and 0.2% Mn, the spectra in the range
m−1 were deconvoluted into A1(1), A2(2), B1, E(5),
E(6) modes at 25 ◦C and 290 ◦C. Fig. 6(a) shows the
ed spectrum of 0% Mn at 25 ◦C. Compared with the
as given in Tables 1 and 2, the A1(1) mode exhibits
shift (from 130 to 102 cm−1) and its broad width
increase in the effective mass of the cations and the
isorder, respectively. Note that the atomic mass of bar-
137.34 amu) lies between the atomic mass of sodium
9 amu) and bismuth (mBi = 208.98 amu). Major dif-
hat A1(2) mode is accompanied by another mode at
This mode is identified as B1, which is characteris-
n in the tetragonal phase [28,34,40]. This gives an
r two phase coexistence in 0% Mn-doped BN7.5BT.
shows the spectra for 1 and 2%Mn deconvoluted into
t modes at 25 and 290 ◦C. The identified modes are
ortho-1–5. The frequencies of Raman modes at 25 ◦C
for differen
of A-O mo
tions remai
frequencies
of the B-si
occupy B-s
Fig. 7 sh
modes as a
Mn, all fre
softening b
uous chang
in ferroelec
structural p
previous w
coexistence
phases to te
Fig. 7(b
quencies fo
softening p
The freque
vibration m
and 18.7 cm
that the so
behavior su
ture. Fig. 8
half maxim
modes (A1tions from 25 to 300 ◦C.t compositions are given in Table 2. The frequencies
des (A1(1) and ortho-1) for all Mn-doped composi-
ns almost the same. The decrease in other vibration
is caused by increase in the effective atomic mass
te cations. This indirectly confirms that the Mn ions
ite of the perovskite unit cell.
ows the frequency shifts of several noticeable Raman
function of temperature. As shown in Fig. 7(a) for 0%
quency modes of A1(2), B1, A1(4), and E(6) exhibit
ehavior with a minimum near 190 ◦C. The discontin-
e in vibration frequency indicates a phase transition
trics [23,24,41], suggesting that 0% Mn undergoes a
hase transition near 190 ◦C. It is consistent with our
ork that 0% Mn undergoes a phase transition from
of rhombohedral R3c and tetragonal P4bm (R + T)
tragonal phase near 200 ◦C [5].
–d) shows temperature dependency of Raman fre-
r 0.2, 1, and 2% Mn. All modes show only slow
ossibly due to freezing-in of Ti/Mn O vibrations.
ncy variations (from 25 to 290 ◦C) of dominant B–O
odes (A1(2) and ortho-2) are respectively, 25.3, 24.3,
−1 for 0.2% Mn, 1% Mn, and 2% Mn, implying
ftening behavior decreases as Mn increases. This
ggests that Mn doping stabilizes the existing struc-
(a–d) shows the temperature-dependent full-width at
a (FWHM) of various Raman modes. B O vibration
(2), B1, νortho-2 and ortho-3) are weakly affected by
temperatur
and ortho-5
dependenc
anhormoni
of unit cell
Synchro
relate it w
evolution
sharper and
symmetry.
tion peaksFig. 10. (2 0 0) peaks with fits (Gauss + Lorenz profiles) at 25, 100, 2
e. The high-frequency modes (A1(4), E(6), ortho-4,
) of BO6 octahedra show significant temperature
e as Mn increases, possibly associated with thermal
city due to random occupation of Mn ions in the B-site
.
tron XRD analysis was carried out in order to cor-
ith Raman spectra. Fig. 9 shows the temperature
of (2 0 0) Bragg’s reflections. The peaks become
move to the lower 2θ position, signifying increasing
In order to understand the phase transitions, diffrac-
were fitted using Gaussian + Lorenzian profile as
shown in F
imental da
temperatur
[2 0 0]T pea
resent rhom
increases, t
In 0% Mn,
tetragonal p
structural p
near 200 ◦C
to 300 ◦C a00, and 300 ◦C for 0 and 0.2% Mn.
igs. 10 and 11. The circles in blue represent the exper-
ta and red solid lines are sums of the fits. At room
e, the (2 0 0) reflection contains [0 0 2]T, [2 0 0]R, and
ks for 0 and 0.2% Mn. The subscripts R and T rep-
bohedral and tetragonal structures. As temperature
he (2 0 0) reflections become sharp and symmetric.
the [2 0 0]R peak vanishes above 200 ◦C and only two
eaks persist. This suggests that 0% Mn undergoes a
hase transition from coexistence to tetragonal phase
. Similarly, in 0.2% Mn the [2 0 0]R peak persists up
s shown in Fig. 10.
All the
marked wi
lower 2θ◦,
waves from
ence of po
in relaxor
also displac
rounding la
than the c
waves from
form Brag
tive interfeFig. 11. (2 0 0) peaks with fits (Gauss + Lorenz profiles) at 25, 100,
XRD reflections have additional peaks, which are
th black dashed lines. These extra peaks appear at
indicating a coherent superimposition of diffracted
nanostrucutres [42,43]. It is known that the exist-
lar nanoregions (PNRs) is a common phenomenon
systems. These are not only polarized regions, but
ed along the direction of polarization from their sur-
ttices. When the PNRs sizes are significantly smaller
oherence length of diffraction radiation, scattered
individual nanoregions coherently superimpose to
g reflection peaks, where constructive and destruc-
rences lead to significant change in the peak profiles
[43]. Thes
face layer,
accommod
experiment
in the relax
the bulk, w
tice. The pr
significantl
the room te
indicated b
peaks as s
Raman spe200, and 300 ◦C for 1 and 2%Mn.
e reflections could also be possible from the sur-
which are often expected in relaxor ferroelectrics to
ate the lattice distortion [44,45]. Neutron diffraction
s [44] showed the existence of near-surface regions
ors, and these regions exhibit larger strain than inside
hich is an indicative of substantial distortion in the lat-
esence of larger strain in the surface layer, contribute
y to the total diffraction profiles. In 1% and 2% Mn,
mperature orthorhombic phase persists up to 300 ◦C,
y the presence of [0 0 2]orth, [0 2 0]orth, and [2 0 0]orth
hown in Fig. 11. These results are consistent with
ctra which showed structural phase transition around
190 ◦C for 0% Mn and only gradual softening behavior up to
290 ◦C for 0.2, 1, and 2% Mn, as shown in Fig. 7(a–d). These
results sug
to hard cha
4. Conclu
We have
ferroelectri
rium of diva
High-resol
coexistence
tures in 0 a
(O) structu
ature. The 0
phase from
panied wit
0.2–2% Mn
heating. Th
tural therm
softening b
Acknowled
This pro
nology of
103-2221-E
Light sour
Office of B
Energy und
Reference
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ang Q
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% Mn-doped BN7.5BT shows a structural transition
coexistence (R + T) to T phase near 190 ◦C, accom-
h a softening anomaly in Raman spectra. Similarly,
-doped BN7.5BT show softening near 290 ◦C upon
is study suggests that Mn ions can enhance struc-
al stability toward higher temperature as revealed by
ehavior of Raman modes.
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