Depolarization in ferroelectric materials has been studied since the 1970s, albeit quasi-statically. The dynamics are described by the empirical Merz law, which gives the polarization switching time as a function of electric field, normalized to the so-called activation field. The Merz law has been used for decades; its origin as domain-wall depinning has recently been corroborated by molecular dynamics simulations. Here we experimentally investigate domain-wall depinning by measuring the dynamics of depolarization. We find that the boundary between thermodynamically stable and depolarizing regimes can be described by a single constant,
P
r
/
ε
0
ε
ferro
E
c
. Among different multidomain ferroelectric materials the values of coercive field,
E
c
, dielectric constant,
ε
ferro
, and remanent polarization,
P
r
, vary by orders of magnitude; the value for
P
r
/
ε
0
ε
ferro
E
c
however is comparable, about 15. Using this extracted universal value, we show that the depolarization field is similar to the activation field, which corresponds to the transition from creep to domain-wall flow.
The purpose of this systematic review is to evaluate the state-of-the-art of competency measurement methods with an aim to inform the creation of reliable and valid measures of student mastery of competencies in communication, lifelong learning, innovation/creativity and teamwork in engineering education. We identified 99 studies published in three databases over the last 17 years. For each study, purpose, corresponding methods, criteria used to establish competencies, and validity and reliability properties were evaluated. This analysis identified several measurement methods of which questionnaires and rubrics were the most used. Many measurement methods were found to lack competency definitions and evidence of validity and reliability. These show a clear need for establishing professional standards when measuring mastery of competencies. Therefore, in this paper, we propose guidelines for the design of reliable and valid measurement methods to be used by educators and researchers.
We demonstrate that trimethylamine borane can exhibit desirable piezoelectric and pyroelectric properties. The material was shown to be able operate as a flexible film for both thermal sensing, thermal energy conversion and mechanical sensing with high open circuit voltages (>10 V). A piezoelectric coefficient of d33≈10–16 pC N−1, and pyroelectric coefficient of p≈25.8 μC m−2 K−1 were achieved after poling, with high pyroelectric figure of merits for sensing and harvesting, along with a relative permittivity of ϵ33σ≈
6.3.
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