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Lead Magnesium Niobate (PMN) System. Important Perovskite End Members for Relaxors Important Relaxors Based on MPB Compositions.

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Presentation on theme: "Lead Magnesium Niobate (PMN) System. Important Perovskite End Members for Relaxors Important Relaxors Based on MPB Compositions."— Presentation transcript:

1 Lead Magnesium Niobate (PMN) System

2 Important Perovskite End Members for Relaxors Important Relaxors Based on MPB Compositions

3 Lead Magnesium Niobate (PMN) System Relaxor-Based Compositions for MLC

4 Lead Magnesium Niobate (PMN) System ApplicationExample Pyroelectrics Capacitors/dielectrics Electrostriction/actuators Medical ultrasound/high efficiency transducers Piezoelectrics Electrooptics Pb(Sc 1/2 Ta 1/2 )O 3 (Ba 0.60 Sr 0.40 )TiO 3 Pb(Mg 1/3 Nb 2/3 )O 3 Pb(Zn 1/3 Nb 2/3 )O 3 Pb[(Mg 1/3 Nb 2/3 ) 1-x Ti x ]O 3 Pb[(Zn 1/3 Nb 2/3 ) 1-x Ti x ]O 3 Pb[(Sc ½ Nb ½ ) 1-x Ti x ]O 3 Pb(Zr 1-x Ti x )O 3 Pb[(Zn 1/3 Nb 2/3 ) 1-x Ti x ]O 3 Pb[(Sc ½ Nb ½ ) 1-x Ti x ]O 3 (Pb 1-x La 2x/3 )(Zr 1-y Ti y )O 3 Areas of Applications for Relaxors Ferroelectrics and Solid Solutions

5 Lead Magnesium Niobate (PMN) System Relaxor Ferroelectrics  Pb(B 1 B 2 )O 3 (B 1 ~ lower valency cation : Mg 2+, Zn 2+, Ni 2+, Fe 3+ ) (B 2 ~ higher valency cation : Nb 5+, Ta 5+, W 6+ )  PMN  Pb(Mg 1/3 Nb 2/3 )O 3  Important Relaxor Ferroelectric with T c ~ -10 C Broad diffused and dispersive phase transition on cooling below T c Very high room temperature dielectric constant Strong frequency-dependent dielectric properties  Nano-scaled compositional inhomogeniety  Chemically order-disorder behavior observed by TEM study  B-site 1:2 order formula with 1:1 order arrangement in the structure (Most have rhombohedral symmetry due to slight lattice distortion)

6 Lead Magnesium Niobate (PMN) System Dielectric properties of Pb(Mg 1/3 Nb 2/3 )O 3 showing diffused phase transition and relaxor characteristics (T max ( at 1 kHz) ~ -10 C with  r max ~ 20,000)

7 Lead Magnesium Niobate (PMN) System PropertyNormal FerroelectricsRelaxor Ferroelectrics Permittivity temperature dependence Permittivity frequency dependence Permittivity behavior in Paraelectric range Remnant polarization (P r ) Scattering of light X-Ray diffraction Sharp 1 st or 2 nd order transition about T c Weak frequency dependence Follow Curie-Weiss Relation above T c Strong remnant polarization Strong anisotropy (birefringent) Line splitting (cubic to tetragonal) Broad-diffused phase transition about T max Strong frequency dependence Follow Curie-Weiss Square Relation above T max Weak remnant polarization Very weak anisotropy to light (pseudo-cubic) No line splitting (pseudo-cubic structure) Comparison of normal and relaxor ferroelectrics

8 Lead Magnesium Niobate (PMN) System First-Order Phase TransitionSecond-Order Phase Transition Spontaneous polarization (P s )  A discontinuity in the first-order phase transition   A continuous change in the second-order phase transition  Relaxor ferroelectric  P s decays continuously with temperature, but does not follow the parabolic temperature dependence as in the second-order phase transition

9 Lead Magnesium Niobate (PMN) System  Dielectric Behavior  Normal Ferroelectrics Relaxor Ferroelectrics Normal ferroelectrics  the onset of spontaneous polarization occurs simultaneously with the maximum in the paraelectric to ferroelectric phase transition. No P s above the transition temperature with a valid Curie-Weiss Law Relaxor ferroelectrics  Three regimes : Regime I Above dielectric maximum temperature, Regime II Between T d (depolarization temperature) and T max (dielectric transition temperature), and Regime III Below T d

10 Lead Magnesium Niobate (PMN) System Regime I : Electrostrictive region with existence of chemically ordered region with no macro-scale ferroelectric domian  little or no hysteresis Regime II : Freezing-out of macro-domain region in which with decreasing temperature the polar regions grow and cluster  hysteresis is observed and becomes more pronounced with decreasing temperature Regime III : Macro-domain region becomes more stable which results to a large spontaneous polarization and piezoelectric effects with large remnant strain

11 Lead Magnesium Niobate (PMN) System Ordered and Disordered Perovskite Structures

12 Lead Magnesium Niobate (PMN) System Ordered and Disordered Perovskite Structures Fully disorder of the cations in the B-sites occupation  “Normal” ferroelectric materials (such as PZT) Nano-scale order of the cations in the B-sites occupation  “Relaxor” ferroelectric materials (such as PMN)

13 Lead Magnesium Niobate (PMN) System Nano-scale ordered region in disordered matrix 5 nm Pb(Mg 1/3 Nb 2/3 )O 3  Nano-scale ordered region with Mg:Nb = 1:1 (like in NaCl structure)  Non-stoichiometric short range chemical heterogeneity  Different ferroelectric transition temperature regions  Diffused/broad dielectric behavior

14 Lead Magnesium Niobate (PMN) System Dark field TEM images showing nano-scale ordered region in disordered matrix PbSc 1/2 Ta 1/2 O 3 Harmer and Bhalla PbMg 1/3 Nb 2/3 O 3 Randall et al.

15 Lead Magnesium Niobate (PMN) System Features for Ordered and Disordered Ferroelectrics PolarizationDielectric HysteresisBirefringence

16 Lead Magnesium Niobate (PMN) System Features for Ordered and Disordered Ferroelectrics Structural Transition Ferroelectric properties decay with increasing T 

17 Lead Magnesium Niobate (PMN) System Relaxor Ferroelectrics  PMN  Pb(Mg 1/3 Nb 2/3 )O 3  Strong frequency-dependent dielectric properties (T max shifts to higher temperature with increasing frequency) (Dielectric losses are at the highest just below T max )  Dynamical thermal re-orientation of polar regions with frequency (As frequency increases, the polar regions cannot keep up   r  and loss  )  Dielectric relaxation similar to glass (follows a Vogel-Fulcher model)  However, no certain explanation for relaxor ferroelectrics   Freezing of micro-region and chemical fluctuation   Ordered-disordered region   Spin-glass model 

18 Lead Magnesium Niobate (PMN) System One of the difficulties in processing PMN ceramics  Pyrochlore (General formula RNb 2 O 6 where R is a mixture of divalent ions)  Pb 1.83 Nb 1.71 Mg 0.29 O 6.39  formed at C  Paraelectric with room temperature  r of 130  Strong reduction in  r if present as inter-granular region in high  r PMN region (Not very significant if only discrete particles disperse in PMN matrix)  Pure Phase PMN with “Columbite Precursor Method” (MgO + Nb 2 O 5  MgNb 2 O 6  MgNb 2 O 6 + PbO  PMN) Example of Pyrochlore Phase

19 Lead Magnesium Niobate-Lead Titanate (PMN-PT) System Most widely studied relaxor materials  PMN-PT Solid Solutions  High-strain (0.1%) electrostrictive actuators High dielectric constant (  r > 25,000) capacitors

20 Lead Magnesium Niobate-Lead Titanate (PMN-PT) System 0.65 PMN PT  MPB Compositions with normal ferroelectric properties High dielectric constant capacitors  0.90 PMN PT  Relaxor (with T max near room temperature with large dielectric constant) (large “electrostrictive” strain)

21 Lead Magnesium Niobate-Lead Titanate (PMN-PT) System Dielectric Behavior of 0.9PMN-0.1PT Relaxor Ferroelectrics

22 Lead Magnesium Niobate-Lead Titanate (PMN-PT) System Strain-Field Relation of 0.9PMN-0.1PT Relaxor Ferroelectrics

23 Lead Magnesium Niobate-Lead Titanate (PMN-PT) System Electrostriction in Ferroelectric Materials  Basis of electromechanical coupling in all insulators x = ME 2 and x = QP 2 (As compared to x ~ E for piezoelectric effects)  Large in ferroelectrics just above T c due to electrical unstabability of ferroelectrics (PMN, PZN, and PLZT) (because of their diffused transition and possible field-activated coalescence of micropolar region to macrodomain of the parent ferroelectric )  “Electrostrictive Mode” “Field-Biased Piezoelectric Mode”  DC Bias Field  Induced Ferroelectric Polarization  Normal Piezoelectric d 33 = 2Q 11 P 3  33 d 31 = 2Q 12 P 3  33

24 Lead Magnesium Niobate-Lead Titanate (PMN-PT) System Advantages of Electrostriction   Minimal or negligible strain-field dependence hysteresis  (in selected temperature range)  More stale realizable deformation than observed in piezo-ceramics   No poling is required   Longitudinal strain 0.1% in PMN 0.3% in PLZT (La/Zr/Ti = 9/65/35) Disadvantages of Electrostriction   Limited usable temperature range  (due to a strong temperature dependence)  Small deformation at low electric field  (as a result of a quadratic nature of electrostriction)

25 PMN-PT and PZN-PT Single Crystals 1-x PMN – x PT Single Crystals x = 35 for MPB compositions  Large piezoelectric strain > 1%  High electromechanical coupling factor (k 33 > 90%)  Relaxor-based piezoelectric crystals for next generation transducers 1-x PZN – x PT Single Crystals x = 9 for MPB compositions  Large piezoelectric strain ~ 1.7%  High electromechanical coupling factor (k 33 = 92%)  Relaxor-based piezoelectric crystals for high performance atuators

26 PMN-PT and PZN-PT Single Crystals Comparison of field-induced strain for various ceramics and single crystals

27 PMN-PT and PZN-PT Single Crystals

28 Engineered Domain States  Initially the domains are aligned as close as possible to the field direction  Increased polarization in rhombohedral structure  As the field is increased to certain values, the domains collapse to the direction, as a result of rhombohedral-to-tetragonal phase transition  Large increase in polarization, hence piezoelectric properties


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