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Special Group Seminar: A.P. Levanyuk
Start Date: 10/10/2019Start Time: 4:00 PM
End Date: 10/10/2019End Time: 5:00 PM
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Event Description:
Two- phase state and elastic instability in small clamped systems undergoing symmetry changing structural phase transitions.
In all bulk perovskites the paraelectric-ferroelectric transitions are of the first order. The question is what happens with these transitions in films on substrates. For strong first order transition and thick films the answer is known since long ago: two-phase states form. But in perovskites the first order transitions are relatively weak. The prevailing belief here is that a first order transition in bulk turns into second order one due to clamping by substrates. This is based on a Devonshire’s result of his 1951 article on BaTiO3. We contribute to discarding this result and development of consistent Landau-like theory of clamped systems that exhibit first order transition in unclamped state. The simplest case is laterally clamped films with two surfaces in the same conditions, being either free or even clamped in a special way. Here 1D approximation is relevant allowing an analytical analysis for laterally finite but relatively large films. Among other results it provides dependence of temperature width of two-phase state on film’s lateral size. For small sizes numerical simulations reveal strong modification of two-phase states. For films on substrates, i.e. with non-equivalent surfaces, no analytical theory of two-phase formation is possible but it is possible to analyze the loss of elastic stability of non-symmetrical phase. Formation of what could be broadly referred to as two-phase states was analyzed numerically. When in equilibrium it occurs in a broader region than the instability. In thin films the forming pattern is sinusoidal resembling that found from the stability analysis. In even thinner films no inhomogeneity forms.
Location Information:
Main Campus - (NANO) Nanoscale Material Science & Engineering Building  (View Map)
Nanoscale Material Science & Engineering Building
731 W. Dickson St.
Fayetteville, Arkansas 72701
United States
Phone: (479) 575-4187
Room: 105
Contact Information:
Name: Laci Shuffield
Phone: 479-575-2506
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