Ferroelectricity. Phase transition. Material properties

Transcription

1 Ferroelectricity. Phase transition. Material properties BaTiO 3 DKDP KDP PZN-PT(9%) PMN-PT(30%) PMN-PT(40%) 4/22/2014 Physics 403 Spring

2 Ferroelectricity. outline Ferroelectricity. Definition Discovery Main properties Phenomenological theory Some materials Relaxors Applications 4/22/2014 Physics 403 Spring

3 Ferroelectricity. Definitions. Ferroelectric Materials. A ferroelectric material is a material that exhibits, over some range of temperature, a spontaneous electric polarization that can be reversed or reoriented by application of an electric field. An American National Standard IEEE Standard Definitions of Primary Ferroelectric Terms 4/22/2014 Physics 403 Spring

4 Ferroelectricity: Discovery Rochelle Salt KNaC 4 H 4 O 6 *4H 2 O 4/22/2014 Physics 403 Spring

5 Ferroelectricity: Discovery Rochelle Salt KNaC 4 H 4 O 6 *4H 2 O Fig3. Piezoelectric response as a function of temperature [2] Fig.1. The first published hysteresis loop [1] Joseph Valasek ( ) University of Minnesota 1. J. Valasek, Phys. Rev. 17, 475 (1921) 2. J. Valasek, Phys. Rev. 19, 478 (1922) 4/22/2014 Physics 403 Spring

6 Ferroelectricity: Two classes of ferroelectrics Order-Disorder Displacement type disorder O Ba P N Ti O O order BaTiO 3 P NaNO 2 4/22/2014 Physics 403 Spring

7 Ferroelectricity: Polarization reversible (P-E hysteresis) PLZST ceramics 40 Sn:Ti = 0.24: P ( C/cm 2 ) E DC (kv/cm) 4/22/2014 Physics 403 Spring

8 Ferroelectricity: Domains + - Single domain state Multi domain state P net ~0 90 o domains Courtesy of Igor Lukyanchuk o domain pattern Y Lu et al. Science 1997;276: /22/2014 Physics 403 Spring

9 Ferroelectricity: Domains PMN-PT40% BaTiO 3 Courtesy of Benjamin Vega-Westhoff and Scott Scharfenberg, P403, Fall2009 KH 2 PO 4 Courtesy of Allison Pohl, P403, Fall2009 PMN-PT30% BaTiO 3 191K KD 2 PO 4 Crystal from Forschungsinstitut für mineralische und metallische Werkstoffe -Edelsteine/Edelmetalle 4/22/2014 Physics 403 Spring

10 Ferroelectricity: Landau-Ginzburg phenomenological theory Free energy F P Order parameter (polarization) ap bp cp... EP F 0 P To find the equilibrium solution we need to find the minima of FP by solving the equation: Electric field Ignoring higher terms we can get the linear solution: F ap E P 0 P 1 E a Assuming linear dependence of a on temperature we will have: 1 ( T T c ) and finally we will have Curie-Weiss law C C ( T T ) c 4/22/2014 Physics 403 Spring

11 Ferroelectricity: Landau-Ginzburg phenomenological theory 80 In case of b>) (C>0 also) We will have the solution for second order phase transition with two equilibrium points p 0 and p 0. Both F (a.u.) E=0 T>T c T=T c these states are equivalent 20 T<T c p 0 P (a.u.) p 0 4/22/2014 Physics 403 Spring

12 Ferroelectricity: Landau-Ginzburg phenomenological theory PLZST ceramics Ps Sn:Ti = 0.24: F (a.u.) Ps P (a.u.) P ( C/cm 2 ) Pr F (a.u.) P (a.u.) Ps F P Including EP term can illustrate the P-E hysteretic behavior ap bp cp E DC (kv/cm) EP F (a.u.) /22/2014 Physics 403 Spring P (a.u.) Pr

13 Ferroelectricity: Susceptibility P D E P E E (1 ) E E 0 E For ferroelectrics >>1 and '/ C=1.9*10 5 ; T CW =385.2K Curie-Weiss law: C ( T ) T CW T (K) 4/22/2014 Physics 403 Spring

14 Ferroelectricity: Typical ferroelectric materials KH 2 PO 4 E DC =1.2kV/cm Courtesy Max Candocia, P403 Spring /22/2014 Physics 403 Spring

15 Ferroelectricity: Typical ferroelectric materials BaTiO 3 cubic rhombohedral orthorhombic tetragonal 4/22/2014 Physics 403 Spring

16 Ferroelectricity: Typical ferroelectric materials T C (K) Ps ( C/cm 2 ) KDP type KH 2 PO KD 2 PO RbH 2 PO Perovskites BaTiO KNbO PbTiO >50 LiTiO LiNbO Number of publications concerning ferroelectricity. From Jan Fousek Joseph Valasek and the Discovery of Ferroelectricity Number of ferroelectric substances discovered in each year. Springer Handbook of Condensed Matter and Materials Data 4/22/2014 Physics 403 Spring

17 Antiferroelectrics <P> ~0 PNZST (film) PLZST (ceramic) Courtesy of E. Colla and City University of Hong Kong 4/22/2014 Physics 403 Spring

18 Antiferroelectricity in BaTiO 3 Courtesy of Alan Selewa and Nathaniel Scheidler (2014, unpublished) 4/22/2014 Physics 403 Spring

19 Ferroelectricity: Relaxors - PMN Pb(Mg 1/3 Nb 2/3 )O '/ / ' T (K) Temperature dependencies of the real part of the dielectric constant measured in a broad frequency range: 3* Hz [1,2] E.V. Colla et all., J. Phys.: Cond. Matter, 4,3671, (1992) 2. E.V. Colla et all. J. Appl. Phys., 83, 3298, (1998) '/ f (Hz) Frequency dispersion of e at different temperatures 4/22/2014 Physics 403 Spring K 220K 250K 240K

20 Ferroelectricity: Solid solution relaxor-regular ferroelectric. (PMN) 0.7 (PT) 0.3 (PMN) (1-x) (PT) (x) phase diagram PT: PbTiO 3, ferroelectric with Curie temperature 763K Paraelectric (cubic) T c (K) 500 Literature data single crystals ceramics Regular ferroelectric (tetragonal) (PMN) 0.6 (PT) x (PMN) 0.9 (PT) 0.1 Relaxor state (PMN) 0.7 (PT) 0.3 (pseudocubic) 4/22/2014 Physics 403 Spring

21 Ferroelectricity: Relaxors - some aplications Actuators Transducers Adaptive optics Capacitors Line motors for SFM Transducer stack for ultrasonic sonar application (TRS Ceramics) Material Dielectric constant Piezoelectric coefficient, (pc/n) Electromechanical coupling factor Quartz Rochelle salt (30C) Barium titanate ceramic Lead zirconate titanate PZT 45/55 PMN-PT (sc) PZN-PT (sc) Piezoelectric properties of different materials 4/22/2014 Physics 403 Spring