Acoustic properties of PZN-x%PT single crystals probed by micro- - PowerPoint PPT Presentation

Acoustic properties of PZN-x%PT single crystals probed by micro- Brillouin scattering Jae-Hyeon Ko 1 *, Do Han Kim 2 , Seiji Kojima 2 1 Department of Physics, Hallym University, Chuncheon, Gangwondo, Korea 2 Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki, Japan * Corresponding author: hwangko@hallym.ac.kr 한국물리학회 2005 년 가을 학술발표회 전북대학교

I. What is relaxor ferroelectrics? � Existence of nanopolar clusters at high temperatures below the Burn’s temperature � Diffused, rounded and frequency-dependent dielectric constant � No overall macroscopic change of the symmetry in many compounds � Dipolar glass model random field model PbMg 1/3 Nb 2/3 O 3 SRBRF model … 한국물리학회 2005 년 가을 학술발표회 전북대학교

Examples of Ferroelectric Relaxors � Complex Perovskites B-site complex Lead magnesium/zinc niobate PbMg 1/3 Nb 2/3 O 3 , PbZn 1/3 Nb 2/3 O 3 Lead scandium/magnesium tantalate PbSc 1/2 Ta 1/2 O 3 , PbMg 1/2 Ta 1/2 O 3 (cf: BaMg 1/2 Ta 1/2 O 3 ) A-site complex Lead lanthanum zirconate titanate (Pb 1-x La x )(Zr y Ti 1-y )O 3 (PLZT100(x/y/1-y)) � Tungsten bronze structure compositions Strontium barium niobate Sr 1-X Ba X Nb 2 O 6 한국물리학회 2005 년 가을 학술발표회 전북대학교

Complex Perovskite Relaxors � Relaxor-based complex perovskite ferroelectrics: � Pb[(Zn 1/3 Nb 2/3 ) 1-x Ti x ]O 3 (PZN-x%PT) � Pb[(Mg 1/3 Nb 2/3 ) 1-x Ti x ]O 3 (PMN-x%PT) � outstanding piezoelectric properties when the electric field is along non-polar direction like [001] - strain level ~ 1.7 % - electromechanical coupling constant > 90% � promising materials for electromechanical applications like actuators, transducers… � superior to PZT due to the single crystal form 한국물리학회 2005 년 가을 학술발표회 전북대학교

* Park et al ., J. Appl. Phys. 82 (1997) 1804. 한국물리학회 2005 년 가을 학술발표회 전북대학교

Phase Diagram of PZN-x%PT ? K. Ohwada et al., PRB 67 094111 (2004) � 한국물리학회 2005 년 가을 학술발표회 전북대학교

• What is the E-T phase diagram of PZN-9%PT, and what are the differences compared to that of PZN- 8%PT? • What changes would be expected from the field effects on the relaxor behaviors of PZN-4.5%PT? 한국물리학회 2005 년 가을 학술발표회 전북대학교

II. Experimental Details: (1) Tandem multi-pass Fabry-Perot interferometer • Sandercock-type tandem 6-pass Fabry- Perot Interferometer • micro-Brillouin scattering system ( ) ( ) λ 514.5 nm * 10 mm 4 f 4 = < µ � d 10 m π π 0 D 1.0 mm L 한국물리학회 2005 년 가을 학술발표회 전북대학교

Light scattering from condensed Matters K i , ω i K i q K f R K f , ω f θ π θ 4 n = = q 2 k sin sin λ i 2 2 i ⎡ ⎤ 4 I k 1 +∞ ∫ ω = < δε δε > ω − ω o f ⎢ ⎥ ( , q , ) ( ,0) ( , ) exp ( ) I R dt q q t i t π ε π if f if if f i ⎢ 2 2 2 ⎥ −∞ 16 R 2 ⎣ ⎦ 0 � Dielectric constant fluctuations of wave vector q and frequency ω determines the scattering event in the experiment. What causes the fluctuations in the dielectric constant? 한국물리학회 2005 년 가을 학술발표회 전북대학교

Brillouin scattering in solids Raman spectroscopy – optic phonons = ∑ 1 − δε ε ( , ) r t p ( , ) r t αβ αβ γλ γλ ε , 2 γλ 0 Sound velocity v Elastic stiffness coefficient c ij = ρ v 2 Elasto-optic constants p αβ,γλ v Brillouin spectroscopy – acoustic phonons 한국물리학회 2005 년 가을 학술발표회 전북대학교

II. Experimental Details: (2) PZN-x%PT single crystals • two compositions x = 4.5%, 9% [100]/[010]/[001] ITO coating for DC field (E // [001]) • either ZFH(zero-field- heating)/ZFC(zero-field cooling) or FC(field- cooling) scan during cooling • backscattering geometry PZN-4.5%PT PZN-9%PT 한국물리학회 2005 년 가을 학술발표회 전북대학교

III. Results (1) – temperature dependence of Brillouin spectra of PZN-x%PT under ZFH/ZFC transverse acoustic mode ZFH process o C 21 • Typical Brillouin spectra consisted of one longitudinal acoustic (LA) mode, one Intensity (arb. unit) weak transverse acoustic (TA) mode and a central peak (CP), where the TA mode o C 85 is noticeable only in the low-temperature rhombohedral phase below 73 o C. • From a symmetrical point of view, the o C 90 TA mode is not allowed at the present scattering geometry in both cubic and tetragonal phases. -60 -40 -20 0 20 40 60 Frequency (GHz) longitudinal acoustic mode 한국물리학회 2005 년 가을 학술발표회 전북대학교

PZN-4.5%PT PZN-9%PT 46 43 cooling Cooling 45 Heating heating Brillouin Shift (GHz) Frequency (GHz) 42 44 41 43 42 40 41 300 350 400 450 500 550 0 200 400 600 800 Temperature (K) Temperature (K) • two phase transitions from cubic • broad softening accompanied to tetragonal, and then to by broad phonon damping, typical rhombohedral phases on cooling behaviors in relaxor ferroelectrics • Clear hysteresis in two phase transition temperatures 한국물리학회 2005 년 가을 학술발표회 전북대학교

III. Results (2) – Field cooling effects on the Brillouin spectra of PZN-9%PT • The temperature range of the tetragonal phase is significantly extended into both high- and low-temperature sides under the electric field along the [001] direction. • The discontinuity at T C − T under ZFC process is smeared out during the FC process as the amplitude of the biasing electric field increases. • The phonon damping has been greatly suppressed by the application of the poling field probably due to the marked decrease of scattering at domain walls. 한국물리학회 2005 년 가을 학술발표회 D. H. Kim et al., JAP 98, 044106 (2005) 전북대학교

E-T phase diagram of PZN-9%PT 8 E // [001], q // [001] Electric Field (kV/cm) 6 4 R T C 2 or X 0 0 50 100 150 200 250 o C) Temperature ( • A E-T phase diagram of PZN-9%PT can be constructed from the present study by observing the changes of the frequency shift as a function of the temperature under the constant biasing field or of the biasing field at a constant temperature. • The change of the Curie temperature (Tc) under the applied field gives the values of dTc/dE ~ 7.8 × 10 − 3 K cm/V and -5.8 × 10 − 3 K cm/V for T C-T and T T-R phase boundaries, respectively. 한국물리학회 2005 년 가을 학술발표회 전북대학교

III. Results (3) – Field cooling effects on the Brillouin spectra of PZN-4.5%PT • two field-induced anomalies at 143 and 106 o C under the electric field of ~ 10kV/cm along [001] • consistent with dielectric data, which reports two phase transitions from cubic to tetragonal, and then to rhombohedral on cooling • may be explained by two-step phase transitions from paraelectric E // [001] phase to microdomain structure, and then from micro- to macrodomain structures upon cooling D. H. Kim et al., APL 87, 072908 (2005) 한국물리학회 2005 년 가을 학술발표회 전북대학교

M. Shen et al., APL 83, 731 (2003) Medium-range ordered phase between the long- range and short-range ordered phases ? 한국물리학회 2005 년 가을 학술발표회 전북대학교

III. Results (4) – Micro-heterogeneity of PZN-4.5%PT • Clear positional dependence of acoustic properties at low temperatures • Existence of micro-heterogeneity over a D. H. Kim et al., APL 87, 072908 (2005) length scale of at least a few microns ? 한국물리학회 2005 년 가을 학술발표회 전북대학교

PZN-4.5%PT Bdikin et al., APL 83, 4232 (2003) (001)-oriented (111)-oriented 한국물리학회 2005 년 가을 학술발표회 전북대학교

IV. Conclusion • Electric field-temperature phase diagram of PZN-9%PT has for the first time been suggested based on the change of acoustic properties upon the application of dc bias field probed by Brillouin scattering experiment, which showed differences from that of PZN-8%PT. • Clear microheterogeneity has been observed in PZN-4.5%PT, which might be related to the complex domain structure of this composition. • Two step anomalies in acoustic properties have appeared in PZN-4.5%PT upon field-cooling, consistent with dielectric measurements. This may signify two-step transformations from paraelectric phase to microdomain structure, and then from micro- to macrodomain structures upon cooling. 한국물리학회 2005 년 가을 학술발표회 전북대학교

Acknowledgments • This research was supported by Hallym University Research Fund, 2005 (HRF-2005-23). • This work was supported in part by the 21st Century COE (Center of Excellence) Program, ”Promotion of Creative Interdisciplinary Materials Science for Novel Function” under MEXT (the Ministry of Education, Culture, Sports, Science and Technology), Japan. 한국물리학회 2005 년 가을 학술발표회 전북대학교

PMN-35%PT 30 o C F. Jiang and S. Kojima, APL 77, 1271 (2000) 한국물리학회 2005 년 가을 학술발표회 전북대학교

한국물리학회 2005 년 가을 학술발표회 전북대학교