Dynamic Evolution of Polar Regions in KTa0.56Nb0.44O3 near the

Subscriber access provided by United Arab Emirates University | Libraries Deanship

Article 0.56

0.44

3

Dynamic evolution of polar regions in KTa Nb O near para-ferroelectric phase transition

Yu Wang, Xiangda Meng, Hao Tian, Chengpeng Hu, Ping Xu, Peng Tan, and Zhongxiang Zhou Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b01576 • Publication Date (Web): 03 Jan 2019 Downloaded from http://pubs.acs.org on January 11, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design

Dynamic evolution of polar regions in KTa0.56Nb0.44O3 near para-ferroelectric phase transition Yu Wang†a, Xiangda Meng†a, Hao Tian*a, Chengpeng Hua, Ping Xub, Peng Tana and Zhongxiang Zhou*a aDepartment bSch

of Physics, Harbin Institute of Technology, Harbin 150001, China.

Chem & Chem Engn, MIIT Key Lab Crit Mat Technol New Energy Convers, Harbin Institute

of Technology, Harbin 150001, China. KEYWORDS: KTN single crystals, para-ferroelectric phase transition; Raman scattering spectrum; polar regions

ABSTRACT: The evolution of domains, which reveals the special structure in the vicinity of paraferroelectric phase transition, is the key to explaining the excellent properties of ferroelectric materials. However, although existing studies offer insight into the process of para-ferroelectric phase transition, questions remain regarding the intermediate structure in order-disorder state. To investigate this phenomenon, we study the stability and intensity of polarization for the temperature-dependent microstructure, deduced from the vibrations of ions. The evolution of polarization and orientation in the polar regions is investigated through the vibrations of the deformation of the octahedral units. In addition, the intensity and full width at half maximum (FWHM) of the B1+E(3TO) mode revealed the stability of polar regions in the dynamic process, 1

ACS Paragon Plus Environment

Crystal Growth & Design 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

which differentiates the static state and dynamic state. Such findings will have a significant impact in the field of property manipulation.

1. INTRODUCTION Solid solution perovskite materials are a topic of interest in the study of the ferroelectric materials,1,2 originating from their advantageous piezoelectric properties, electrostrictive performance, and electro-optical nature in the vicinity of phase transition.3-8 The ferroelectric materials have stable properties in different phases, which are far away from the phase transition temperature.9 However, the intermediate structure cannot be deduced from the stable phase state in the critical region of the phase transition, as the feature structure of the adjacent phase conditions is different.10-16 On a microscopic scale, the competition and coexistence between short-range and long-range polar order exist simultaneously. The conventional idea is that the polar nano-regions (PNRs) appear at high temperatures, beyond the Curie transition, and form nuclei for the fieldinduced long-range order at low temperatures.17 However, the dynamic process and changing mechanism of the polar regions could not be explained properly. Potassium tantalate niobate (KTa1-xNbxO3, KTN), as a typical perovskite solid solution of KTaO3 and KNbO3, is investigated. Its nonlinear scale-free propagation without distortion in out-of-equilibrium based on the control of PNRs in lithium doping.18 For KTN, it is widely believed that the spontaneous polarization of polar regions is induced by the off-center displacements of niobium ions at the B-site near the Curie temperature (TC).19 However, the contribution for the deformation of the octahedral units, which also offers polarization, could not be ignored. 2


Page 2 of 21

Page 3 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In this work, the contribution of the polarization for the different vibrations of the KTa0.56Nb0.44O3 single crystal was studied through the Raman scattering spectrum. The measured ratio of the elements of the Raman tensors shows the anisotropy of vibration of the A1 symmetry, which demonstrates the off-center displacements of niobium ions providing the anisotropic polarization. The dynamic evolution of polar regions in KTa0.56Nb0.44O3 was clearly observed, where polar regions undergo the static domains, relaxational polar regions with the frequency dispersion of the relative dielectric constant, permanent correlative PNRs, dynamic PNRs, and disappearance of PNRs near the para-ferroelectric phase transition. It is worth noting that the B1+E(3TO) mode and the A1(3TO) mode are related to the intensity and the orientation of the polar regions. 2. EXPERIMENTAL PROCEDURE The top seeded solution growth (TSSG) method was used to grow the high-quality KTa0.56Nb0.44O3 single crystal.20 The crystal was cut into a cube with a size of 1.04×3.83×1.69 mm3 ([100]Cx  [010]Cy  [001]Cz ) , with the (100) surface polished. The silver electrodes were deposited on the (001) face. The power and wavelength of the incident laser on the sample were 1 mW and 633 nm, respectively. The scattered light was collected at a back-scattering geometry and analyzed by a Renishaw inVia confocal micro-Raman spectroscopy system using a TE air-cooled 576 × 400 CCD array. The geometric configurations were expressed by the Porto’s notation, i.e., a(bc)a (VH), where a, a , b, and c represent the direction of propagation for incident light,

scattered light, and the polarization of incident and scattered light, respectively. The temperature of the samples was controlled by the heating/cooling stage (Linkam, THMS600) with ± 0.1 °C 3



accuracy over all temperatures. To determine TC, the temperature dependence of the relative dielectric permittivity (  r ) was measured with an LCR meter (E4980A, Agilent Technologies). Powder X-ray diffraction (XRD) data was collected by a diffractometer (PANalytical Empyrean) with a Cu-Kα radiation tube at 40 kV and 40 mA with a step size of 0.0001º, and the contribution of Cu-Kα2 was removed by the software called MDI Jade. 3. RESULTS AND DISCUSSION At room temperature, the structure of the KTa0.56Nb0.44O3 in the tetragonal phase is in P4mm symmetry, which is confirmed by the temperature dependence of the relative dielectric permittivity (  r ), as shown in Figure 1a.

Figure 1. (a) The temperature-dependence of the relative dielectric permittivity (  r ) measured at 100Hz, 1 kHz, 10 kHz, 100 kHz and 500Hz for KTa0.56Nb0.44O3. The inset shows the frequency dispersion of the relative 4


Page 4 of 21

Page 5 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


dielectric constant at Tf and T*. (b) The temperature-dependence of the  r1 and the fit line at high temperatures, and in the vicinity above the TC. (c) Raman scattering spectrum and the fitting line in the configurations of VH, with the polarized sample along the direction of [001]C. (d)–(g) The sketch map for the A1(2TO), A1(3TO), B1, and E(3TO) mode, respectively.

In the KTN, the internal vibrations originate from the translational modes of K+ cations and the internal modes of NbO6/TaO6 octahedral units. It contains 15 vibrational modes, including three acoustic modes and 12 optical modes. The optical vibrational modes of KTN in the tetragonal phase can be represented as follows,

Γopt = 3A1 (R, IR) + B1 (R) + 4E(R, IR)

(1)

Here R and IR denote Raman and infrared radiation activity, respectively, while A1 and B1 show the non-degeneracy mode, and E denotes the double degeneracy mode. Figure 1c shows the Raman spectrum of KTa0.56Nb0.44O3 at room temperature. To analyze the vibrations of KTa0.56Nb0.44O3, the spectrum was fitted by the combination of a Lorentzian central peak (CP),21 damped harmonic oscillator (DHO) model, and a third order polynomial with the Fano function as22,23

I r ( ) 

CP 2 ACP Ai ii2 I 0 (q   )2    I i ( 2   2 )2   2 2 B (1   2 ) 2 π 4 2  CP i i

(2)

Here ACP and ΓCP are the intensity and FWHM of the CP, respectively. Ai, Гi, and ωi are intensity, damping,

and

frequency

of

the

ith

Raman

mode,

respectively.

I B  P(  TO2 )3  Q(  TO2 ) 2  R(  TO2 )1  S has the constants P, Q, R, and S, and I0 is intensity of the Fano resonance (TO2 mode), q is the asymmetry parameter, and  =



2  - TO2



 TO2

is the reduced energy.  TO2 is the FWHM of the Fano resonance. The spectrum was fitted into the sum of 10 Lorenz peaks at 140 cm-1, 172 cm-1, 228 cm-1, 278 cm-1, 300 cm-1, 535 cm-1, 557 5



Page 6 of 21

cm-1, 600 cm-1, 753 cm-1 and 880 cm-1. The A1(1LO) mode at 172 cm-1 can be described as the vibration of the K+ cations versus the NbO6/TaO6 octahedral units.24,25 The A1(2TO) mode at 199 cm-1, which is related to the Fano resonance,26 is where the niobium ions vibrate against the NbO6/TaO6 octahedral units, as shown in Figure 1d. The B1+E(3TO) mode at 278 cm-1 [Figure 1(f-g)] is the wing-flapping vibration of the four oxygen atoms in the same plane. The A1(3TO) mode at 557 cm-1 is the sign of the deformation of the NbO6/TaO6 octahedral units,23 as shown in Figure 1e. The E(2TO) mode, E(4LO) mode, the couple mode of E(3TO) and A1(2TO) appear at 228 cm-1, 880 cm-1 and 753 cm-1, respectively.27 The angular-dependence of the integrated intensity obtained in the VV and VH configuration are shown in Figure 2, with the best-fit curves. At room temperature, the ferroelectric phase belongs to the space group of P4mm, for which the Raman tensors of the observable optic modes can be described as28

 aea   0  0 

0 aea 0

0   c 0 0 0 0 0    0  for A1(z),  0 c 0  for B1 and  0 0 e  for E(y) 0 0 0 0 e 0 beb     

(3)

The angular-dependence of the Raman scattering spectrum integrated intensity was fitted by the following expression 1

1

R  C   A1 ( z )orB1orE ( y )  R  C

(4)

0 0  1   R =  0 cos( )  sin( )   0 sin( ) cos( )   

(5)

Here, C is the transformation matrix for the modification of the Raman tensor components and the R is the rotation matrix. The intensity of VV and VH can be described as follows29

6


Page 7 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2

2

I AP1  a cos 4   b sin 4   2 a b cos  sin 2  cos 2 

I A1 



(6)



1 2 2 a  2 a b cos   b sin 2  4 2

I BP1  c cos 4  , I B1  2

(7)

1 2 2 c sin 2 4

(8)

2

I EP  e sin 2 2 , I E  e cos 2 2

(9)

Here,  is the rotation angle of experimental coordinates and  =b  a represents a relative phase difference between two elements of the A1 mode. The obtained fitting parameters for the A1(2TO) and A1(3TO) modes are shown in Table 1. Table 1 The best fit results of the value, anisotropic ratio, and the phase difference of the Raman tensor with A1 symmetry. φ (degree) a b b/a A1(2TO) A1(3TO)

21 49

70 80

89.5 89.6

3.33 1.63

The matrix element of the Raman tensor can be described as

   Rij   ij   rk rk 0

(10)

Here, rk is the ionic-displacement coordinate and  ij is the dielectric tensor.28

7



Figure 2. The fit line of the angle dependence of the Raman scattering spectrum (a)–(f) for the A1(2TO), A1(3TO), and B1+E(3TO) mode in the VV (left) and VH (right), respectively.

The ratio of b/a indicates the anisotropic ratio of the different phonons, which reveals the different contributions to the Raman susceptibility along the direction of [001]C. The A1(2TO) mode, which is related to the niobium ions versus all the oxygen ions of the NbO6/TaO6 octahedral units parallel to the [001]C direction, has a larger anisotropic ratio of 3.33. It is obvious that the vibration for the off-center displacements of niobium ions prefers to bind electrons in the direction along the [001]C, making a larger contribution to the anisotropic polarization than the deformation of octahedral units (A1(3TO) mode). The B1+E(3TO) mode is more obvious in the configuration of VH than VV, because the Raman tensor of the symmetry of the E(3TO) mode is an off-diagonal matrix. The elements’ value 8


Page 8 of 21

Page 9 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of the Raman tensor of the B1 and E(3TO) mode are 13.5 and 15.5, which is smaller than that of the elements of the A1 mode. This indicates that the vibrations of the niobium ions versus the NbO6/TaO6 octahedral units and deformation of the octahedral units along the [001]C direction are the leading factors in the tetragonal phase.

Figure 3. The temperature-dependence of the Raman spectrum for (a) the region from 150cm-1-1000cm-1 (the data was measured every 2°C in the range of 40 °C to 100 °C), (c) B1+E(3TO) and (d) A1(3TO), respectively. (b) is the Raman spectrum for paraelectric cubic phase, ferroelectric phase and polarized sample, respectively.

The Raman scattering spectrum in Figure 3a shows the temperature-dependence of intensity and FWHM in VH. In the ferroelectric phase, there are two stable solutions with the same absolute value for polarization, revealing that antiparallel static domains can exist, as shown in Figure 5f.30 It can be confirmed by the relationship of the relative dielectric permittivity and temperature at different frequencies, as shown in inset of Figure 1a. The relative dielectric permittivity (  r ) is the same for different frequencies under the Tf, which indicates that the domains are frozen.31 Both 9



Page 10 of 21

the intensity and the FWHM slowly change when the temperature is under Tf. The decresing of intensity shows the weakening of the polarization. The FWHM shows a slow positive correlation with the temperature, discribed by the equation written as     2  3 3    (T )  A 1  h0  h0 +B 1  h0     e 3kBT  1 (e 3kBT  1) 2   e 2 kBT  1 

(11)

Here, A and B are constants and 0 represents the harmonic frequency of the optical mode.32 The change in the FWHM was affected by the expansion of the lattices. It also verified by the temperature-dependence of the X-ray diffraction as shown in Figure 4. The (300) and (003) peaks close to each other with the raising of the temperature, which reveals the weakening of the ferroelectricity. The ferroelectric domains change to the relaxational polar regions above the Tf, which induces the intensity to decline rapidly. This change is caused by the appearance of the third metastable solution for Gibbs free energy, which provides an alterable factor, in the temperature range between Tf and TC, as shown in Figure 5f. This leads to the decrease in intensity of the Raman spectrum, which is caused by the further weakening of polarization (the displacement of ions starts to reduce with the appearance of the zero polarization solution), for both the B1+E(3TO) mode and A1(3TO) mode. Both the steady intensity of the A1(3TO) and the tardy position changing of the (003) and (300) indicate that the intensity of the polarization has the weak correlation with the temperature above the Tf. The temperature mainly acts on the interaction of domains, which breaks the stability of the ferroelectric domains. The FWHM of both the A1(3TO) mode and the B1+E(3TO) mode start to grow rapidly in the vicinity of Tf. This means that the evolution of the domains near the Tf is quasi-static. The interaction of the domains cannot provide the steady consistent orientation, which can be driven by the external electric field. Therefore, the frequency dispersion appears in the temperature-dependence of the relative dielectric permittivity, as shown 10


Page 11 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


in the inset of Figure 1a. All the modes should not be found above the TC (the space group of Pm3m),33,34 according to the Raman selection rules, as a result of the phase transition. However, it is still active for the vibration mode as shown in Figure 3b.

Figure 4. (a) The temperature-dependence of the X-ray diffraction for KTN44. (b) The temperature-dependence of the peak positions of (003) and (300).

The polar regions start to shrink and correlate with each other in the short-range due to the specific polarization not being the static solution for the Gibbs free energy. This influences the vibration for both the B1+E(3TO) mode and A1(3TO) mode, which leads to the drastic change for the temperature-dependence of intensity and FWHM. The change trend of the FWHM for B1+E(3TO) is a sign of the breaking of the quasi-steady state. It is interesting that the intensity stops the changing at the T*, caused by the disordered dynamic PNRs. The coupled polar regions translate to dynamic PNRs with the disappearance of the correlated motion under the local driving force. The abnormity originetes from the contribution of both the angular-dependence and the further weakening of the polarization. The geometric configuration (  =0o in VH) of the mearement is the minimum for the both the B1+E(3TO) mode and A1(3TO) mode in angular-dependence. The disordered orientation will increase the intensity while the weakening of the polarization impairs it. The growth of the FWHM for the B1+E(3TO) mode verifies that the vibration of the oxygen 11



ions in the plane perpendicular to the [001]C direction is unstable. The deformation of the octahedral units would not be influenced in the correlated motion of PNRs, which indicates that the correlated motion affects the orientation of PNRs more than the intensity of polarization. This can be confirmed by the steady region for FWHM between the T* and TB. The slow change of the peak of (300) can also verify it. And the disappearance of the correlated motion of PNRs means that the disappearance of the frequency dispersion in the temperature-dependence of the relative dielectric permittivity because of the response speed of PNRs is enough to reach the different frequency of ac field. Finally, the intensity of both the B1+E(3TO) and A1(3TO) mode decline tardily as a result of the disappearance of PNRs above the TB due to the high symmetry of the structure, as shown in Figure 5e. The disappearance of the PNRs can be verified by the merged of the (300) and (003).

12


Page 12 of 21

Page 13 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. (a)–(e) shows the static domains under the Tf, the quasi-static state, the decreasing correlation of PNRs, the size reduction of the polar regions and the sign of the disappearance of PNRs, respectively. (f) The sketch map of Gibbs free energy with the polarization intensity at different temperatures.

To confirm the course of phase transition, the temperature dependence of the relative dielectric permittivity (  r ) was measured, as shown in Figure 1a. The peak of the dielectric spectrum indicates that the TC of the KTa0.56Nb0.44O3 sample is 57 °C according to the heating. The inset shows the Tf and the T* at 50 °C and 65 °C, with the divarication of lines for different frequencies. Figure 1b shows the inverse dielectric constant versus temperature for the KTa0.56Nb0.44O3 crystal. This reveals that KTa0.56Nb0.44O3, in the cubic phase (paraelectric phase) obeys the Curie–Weiss law, as follows.

 r -1 =

T  T0 C

(12)

Here, C is a costant. The experimental data diverges from the linear relation at the temperatures 65 °C (T*) and 80 °C (TB), according to the line of fit of the region in the vicinity above TC and high temperature, respectively. The results of the temperature dependence of the relative dielectric permittivity is in agreement with the dynamic process analyzed by Raman spectra and XRD. 4. CONCLUSION In summary, the Raman scattering spectrum of KTa0.56Nb0.44O3 reveals the origin of different modes in the tetragonal phase. The ratio of b/a for the A1(2TO) and A1(3TO) modes, triggered from the niobium ions versus the octahedral units and the deformation of octahedral units along the polar direction, respectively, show the anisotropy of the sample in the tetragonal phase. The vibration for the displacement of niobium ions prefers to bind electrons along the direction of [001]C than along the deformation of the octahedral units. The relationship between the Raman spectrum and temperature reveals four characteristic temperatures; Tf, TC, T*, and TB. The 13



polarization is influenced by the increasing temperature in the vicinity of Tf, which can be confirmed by the Gibbs free energy. This reveals the softening of internal vibrational or dynamical degrees of freedom. The region from TC to T* indicates the evolution of the polar regions under the correlative motion in short-range, which indicates by the further weakening of the interaction for polar regions. The nanoscale polar regions become dynamic PNRs above T*, which indicates the disordered state. The steady intensity of the A1(3TO) mode above T* elucidates the randomness of the direction and the weakening of polarization for dynamic PNRs. It means that the interaction of polar regions is not enough to correlate them anymore. However, the distribution of deformation of the octahedral units is not broadened during this process, which shows that the loss of coupled motion mainly effects the orientation of the deformation of the octahedral units. The region above the TB indicates the disappearance of the PNRs with high symmetry, which suppresses the Raman activity.

AUTHOR IMFORMATION Corresponding Author * E-mail: [email protected]. (H. T.) * E-mail: [email protected]. (Z. Z.) Author Contributions Y. Wang and X. Meng contributed equally to the manuscript. Notes 14


Page 14 of 21

Page 15 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The authors declare no competing financial interests. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (NSFC) (1167040679, 50902034).

REFERENCES (1) Scott, J. F. Applications of modern ferroelectrics. Science 2007, 315, 954-959. (2) Deng, H.; Zhao, X.Y.; Zhang, H.W.; Chen, C.; Li, X.B.; Lin, D.; Ren, B.; Jiao J.; Luo, H.S. Orientation dependence of electrical properties of large-sized sodium potassium niobate lead-free single crystals. CrystEngComm 2014, 16, 2760-2765. (3) Tian, H.; Yao, B.; Hu, C.; Meng, X.; Zhou, Z. Impact of polar nanoregions on the quadratic electro-optic effect in K0. 95Na0. 05Ta1− xNbxO3 crystals near the Curie temperature. Appl. Phys. Express 2014, 7, 062601. (4) Pechenyi, A. P.; Glinchuk, M. D.; Azzoni, C. B.; Scardina, F.; Paleari, A. EPR evidence of extrinsic symmetry-breaking defects in nominally pure KTaO3. Phys. Rev. B 1995, 51, 12165.

15



(5) Li, H.; Meng, Q.; Gong, D.; Tian, H.; Zhou, Z. Good temperature stability and high piezoelectric properties of pure and La-doped tetragonal (K0.45Na0.55)0.94Li0. 06TaxNb1−xO3 ceramics. J. Eur. Ceram. Soc. 2014, 34, 4185-4192. (6) Yang, W.; Zhou, Z.; Yang, B.; Zhang, R.; Wang, Z.; Chen, H.; Jiang, Y. Structure and Piezoelectric Properties of Fe-Doped Potassium Sodium Niobate Tantalate Lead-Free Ceramics. J. Am. Ceram. Soc. 2011, 94, 2489-2493. (7) Nakamura, K.; Miyazu, J.; Sasaki, Y.; Imai, T.; Sasaura, M.; Fujiura, K. Space-chargecontrolled electro-optic effect: Optical beam deflection by electro-optic effect and spacecharge-controlled electrical conduction. J. Appl. Phys. 2008, 104, 013105. (8) Zhou, Z.; Li, J.; Tian, H.; Wang, Z.; Li, Y.; Zhang, R. Piezoelectric properties of the leadfree K0. 95Li0. 05Ta0. 61Nb0. 39O3 single crystal. J. Phys. D. Appl. Phys. 2009, 42, 125405. (9) Cochran, W. Crystal stability and the theory of ferroelectricity. Adv. Phys. 1960, 9, 387423. (10)Bitton, G.; Razvag, M.; Agranat, A. J. Formation of metastable ferroelectric clusters in K1−xLixTa1−yNbyO3: Cu, V at the paraelectric phase. Phys. Rev. B 1998, 58, 5282-5286. (11)Ishai, P. B.; De Oliveira, C. E. M.; Ryabov, Y.; Feldman, Y.; Agranat, A. J. Glass-forming liquid kinetics manifested in a KTN:Cu crystal. Phys. Rev. B 2004, 70, 132104.

16


Page 16 of 21

Page 17 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(12)Bobnar, V.; Erste, A.; Chen, X. Z.; Jia, C. L.; Shen, Q. D. Influence of dc bias electric field on Vogel-Fulcher dynamics in relaxor ferroelectrics. Phys. Rev. B 2011, 83, 132105. (13)Li, F.; Xu, Z.; Zhang, S. J. The effect of polar nanoregions on electromechanical properties of relaxor-PbTiO3 crystals: Extracting from electric-field-induced polarization and strain behaviors. Appl. Phys. Lett. 2014, 105, 122904. (14)Li, Q.; Liu, Y.; Cheng, Z.; Bian, J. J.; Chen, H.; Withers, R. L. Observation of short-lived local polar states induced by applied tip biases in BaTiO3-based relaxor ferroelectric ceramics. Appl. Phys. Lett. 2013, 103, 022904. (15)Toulouse, J.; Wang, X. M.; Knauss, L. A.; Boatner, L. A. Dielectric nonlinearity and spontaneous polarization of KTa1−xNbxO3 in the diffuse transition range. Phys. Rev. B 1991, 43, 8297-8302. (16)Kutnjak, Z.; Blinc, R.; Petzelt, J. The giant electromechanical response in ferroelectric relaxors as a critical phenomenon. Nature 2006, 441, 956-959. (17)Xu, G.Y.; Zhong, Z.; Bing, Y.; Ye, Z.-G.; Shirane, G. Electric-field-induced redistribution of polar nano-regions in a relaxor ferroelectric. Nat. Mater. 2006, 5, 134140. (18)DelRe1, E.; Spinozzi1, E.; Agranat, A. J.; Conti, C. Scale-free optics and diffractionless waves in nanodisordered ferroelectrics. Nat. Photonics 2010, 5, 39-42. 17



(19)Hanske-Petitpierre, O.; Yacoby, Y.; De Leon, J. M.; Stern, E. A.; Rehr, J. J. Off-center displacement of the Nb ions below and above the ferroelectric phase transition of KTa0.91Nb0.09O3. Phys. Rev. B 1991, 44, 6700-6707. (20)Tian, H.; Tan, P.; Meng, X.; Hu, C.; Shi, G.; Zhou, Z.; Wang, X. Effects of Growth Temperature on Crystal Morphology and Size Uniformity in KTa1–xNbxO3 and K1– yNayNbO3

Single Crystals. Cryst. Growth Des. 2016, 16, 325-330.

(21)Toulouse, J.; Jiang, F.; Svitelskiy, O.; Chen, W.; Ye, Z.-G. Temperature evolution of the relaxor dynamics in Pb(Zn1∕3Nb2∕3)O3: A critical Raman analysis. Phys. Rev. B 2005, 72, 184106. (22)Yacoby, Y. Defect induced fluctuations in the paraelectric phase of KTa0.94Nb0.06O3. Z. Physik. B 1978, 31, 275-282. (23)Rahaman, M. M.; Imai, T.; Miyazu, J.; Kobayashi, J.; Tsukada, S.; Helal, M. A.; Kojima, S. Relaxor-like dynamics of ferroelectric K(Ta1−xNbx)O3 crystals probed by inelastic light scattering. J. Appl. Phys. 2014, 116, 074110. (24)Kakimoto, K. ; Akao, K.; Guo, Y.; Ohsato, H. Raman scattering study of piezoelectric (Na0.5K0.5) NbO3-LiNbO3 ceramics. Jpn. J. Appl. Phys. 2005, 44, 7064-7067. (25)Sang, S.; Yuan, Z.; Zheng, L.; Sun, E.; Qi, X.; Zhang, R.; Jiang, X.; Li, S.; Du, J. Raman spectra of (K, Na)(Nb, Ta)O3 single crystal. J. Alloy. Compd. 2017, 704, 804-808. 18


Page 18 of 21

Page 19 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(26)Wang, D.; Hlinka, J.; Bokov, A. A.; Ye, Z.-G.; Ondrejkovic, P.; Petzelt, J.; Bellaiche, L. Fano resonance and dipolar relaxation in lead-free relaxors. Nat. Commun. 2014, 5, 5100. (27)Kugel, G. E.; Mesli, H.; Fontana, M. D.; Rytz, D. Experimental and theoretical study of the Raman spectrum in KTa1−xNbxO3 solid solutions. Phys. Rev. B 1988, 37, 5619-5628. (28)Manlief, S. K.; Fan, H. Y. Raman Spectrum of KTa0.64Nb0.36O3. Phys. Rev. B 1972, 5, 4046-4060. (29)Fujii, Y.; Noju, M.; Shimizu, T.; Taniguchi, H.; Itoh, M.; Nishio, I. Raman tensor analysis of crystalline lead titanate by quantitative polarized spectroscopy. Ferroelectrics 2014, 462, 8-13. (30)Ma, C.; Guo, H.; Tan, X. A New Phase Boundary in (Bi1/2Na1/2)TiO3−BaTiO3 Revealed via a Novel Method of Electron Diffraction Analysis. Adv. Funct. Mater. 2013, 23, 52615266. (31)Tan, P.; Tian, H.; Hu, C.; Meng, X.; Mao, C.; Huang, F.; Shi, G.; Zhou, Z. Temperature field driven polar nanoregions in KTa1−xNbxO3. Appl. Phys. Lett. 2016, 109, 252904. (32)Pavunny, S. P.; Kumar, A.; Katiyar, R. S. Raman spectroscopy and field emission characterization of delafossite CuFeO2. J. Appl. Phys. 2010, 107, 013522. (33)Chen, I. W.; Structural origin of relaxor ferroelectrics-revisited. J. Phys. Chem. Solids 2000, 61, 197-208. 19



(34)P. K. Davies, and M. A. Akbas, Chemical order in PMN-related relaxors: structure, stability, modification, and impact on properties. J. Phys. Chem. Solids 2000, 61, 159-166.

20


Page 20 of 21

Page 21 of 21 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


For Table of Contents Use Only Dynamic evolution of polar regions in KTa0.56Nb0.44O3 near paraferroelectric phase transition Yu Wanga, Xiangda Menga, Hao Tian*a, Chengpeng Hua, Ping Xub, Peng Tana and Zhongxiang Zhou*a

The dynamic evolution of the polar-regions in the para-ferroelectric phase transition and the different vibration modes’ contributions to the polarization were discovered by the temperaturedependence and angular-dependence Raman spectrum.

21


Dynamic Evolution of Polar Regions in KTa0.56Nb0.44O3 near the

Recommend Documents