a new model of correlated disorder in relaxor ferroelectrics

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20 Too complex for simple models? phenomenological PNR models introduce low-symmetry objects embedded in cubic matrix •3 parameters: characteristic lengths (ξ α ~ 10 nm) •3 parameters: basis orientation •2 parameters: Pb displacement direction still not enough to reproduce the experimental data • Wrong q-dependence • Does not reproduce 2D maps • Wrong shape in 3D Is something wrong with the structure of models? How can one model diffuse scattering in relaxor without having PNRs?
New parametrization hint: use the analogy with thermal diffuse scattering average symmetry: cubic Pb position: delocalized over sphere 2 2 sin (2πr0 Q) T −1 I ∝ f Pb(Q)exp(-2WPb(Q)) ⋅Q ⋅ Σ( Q) ⋅Q 2 Q Σ Σ Σ pc fcc ( Q) = (1 − µ ) Σ ( Q) + Σ ( Q) αα αα µ pc αα fcc αα Σαβ ( Q) = ( Ψ44 + Ψ12 )sin(2πQα )sin(2πQ β Ψijkl αα ( Q) = 2Ψ (1 − cos(2πQα )) + 2Ψ44 (2 − cos(2πQ ) − cos(2πQ 11 β γ ( Q) = Ψ (2 − cos(2πQα )(cos(2πQ β ) + cos(2πQγ ))) + (2Ψ44 − Ψ12 )) )(1 − cos(2πQ )cos(2πQ 11 β γ is of cubic symmetry: 3 invariants Ψ is not elastic tensor ) analogy with D(Q) for monoatomic lattice )) 2 adjustable parameters: i.e. Ψ 11 /Ψ 12 and Ψ 11 /Ψ 44 ; large q: adjustable µ for the prototype formulae see A. Bosak, D. Chernyshov, Acta Cryst. A 64, 598 (2008)
Page 1 and 2: A NEW MODEL OF CORRELATED DISORDER
Page 3 and 4: Outline Diffuse scattering in rela
Page 5 and 6: Reported DS data 1D: line scans 2
Page 7 and 8: Experiment PbMg 1/3 Nb 2/3 O 3 -Pb
Page 9 and 10: 3D data vs. documented PNR models e
Page 11 and 12: Comparing 2D data… Hiraka et al.
Page 13 and 14: 310 node - 2D and 3D Cervellino et
Page 15: Incomplete input for modeling this
Page 19 and 20: New parametrization: 2D µ = 0.95 s
Page 21 and 22: New parametrization: 3D experiment
Page 23 and 24: Laue TOF vs. X-ray scattering main
Page 25 and 26: Electric field effect experimental
Page 27 and 28: 10 If no polar domains - than what?
Page 29 and 30: Real space model: concept does work
Page 31 and 32: Real space model: displacement patt
Page 33 and 34: Microscopic model behind The set o
Page 35 and 36: X Relaxor-specific component of
Page 37 and 38: X X X Relaxor-specific component
Page 39 and 40: X X X X X Relaxor-specific componen
Page 41 and 42: Conclusions II Diffuse clouds of c
Page 43: Acknowledgments Efim Kats Institut

a new model of correlated disorder in relaxor ferroelectrics

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