Colloquium Schedule

Colloquium: Thursday, January 30th, 4:25 PM, Lewis Lab 316

Ferroelectrics and Ferroelastics far from Equilibrium: Avalanche Spectroscopy

Ekhard K.H. Salje

Cambridge University
Noise generated by mobile ferroelectric domain boundaries is reported for BaTiO3, PST and related materials. Mobile domain boundaries follow the path of crackling noise in a far-from-equilibrium scenario. This noise is measured by acoustic emission signals and, simultaneously, jerks in the depolarization current and in speckle spectra. Noise exponents for the emitted energy E, their maximum amplitudes A, their duration D and the interevent times T will be discussed. Acoustic emission spectroscopy shows that electric-field switching of 90◦ boundaries generates large strain fields, which emit acoustic phonons during ferroelectric hysteresis measurements. We use highly sensitive receivers (microphones) to measure the time sequences of noise in close analogy to noise patterns in ferroelastic and magnetic materials (~ Barkhausen noise). The traditional view is to ask how domain walls move under external forcing. The alternative question is to ask what the probability distribution of the totality of all such moves is. Only the latter approach leads to a global response where the switching properties are determined in a statistical manner. ‘Jerk’ spectra due to acoustic emission (AE), which occurs during ferroelectric avalanches, have seldom been investigated before and current models of avalanche theory have not been applied. With improved technical means this has become possible and full data sets of ferroelectric and ferroelastic noise pattern will be presented.

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Physics and Astronomy Colloquia are usually scheduled for Thursdays at 4:25 PM in Lewis Lab room 316. Refreshments and snacks are available in the nearby coffee room at 4:00 PM.


Physics Colloquium Schedule for Fall 2019

Click on Title below for past or upcoming Announcements (where available), and Speaker name for website.        

January 20---
January 23---
January 30Ekhard K.H. SaljeCambridge UniversityFerroelectrics and Ferroelastics far from Equilibrium: Avalanche Spectroscopy 
February 6---
February 13---
February 20---
February 27Daan FrenkelCambridge University-
March 5---
March 19Antal JevickiBrown University -
March 26William PhillipsNIST-
April 2Edward LymanUniversity of Delaware-
April 9Babak SeradjehIndiana University-
April 16---
April 23Velia FowlerUniversity of Delaware