Interfacial ferroelectricity by van der Waals sliding

Despite their partial ionic nature, many layered diatomic crystals avoid internal electric polarization by forming a centrosymmetric lattice at their optimal van-der-Waals stacking. Here, we report a stable ferroelectric order emerging at the interface between two naturally-grown flakes of hexagonal-boron-nitride, which are stacked together in a metastable non-centrosymmetric parallel orientation. We observe alternating domains of inverted normal polarization, caused by a lateral shift of one lattice site between the domains. Reversible polarization switching coupled to lateral sliding is achieved by scanning a biased tip above the surface. Our calculations trace the origin of the phenomenon to a subtle interplay between charge redistribution and ionic displacement, and provide intuitive insights to explore the interfacial polarization and its unique “slidetronics” switching mechanism.

Introduction to Piezoelectric Actuators: Research Misconceptions and Rectifications - Part II

<p>Piezoelectric actuator developments require interdisciplinary knowledge on materials physics, electrical designing and mechanical engineering. Because of the limited knowledge of newly-involved researchers, they occasionally publish misleading information, some sort of misconceptions, reflected in the delay of innovative developments of the next generation. This paper is Part II of a series of my tutorial course, and reviews the popular 10 among the researchers’ misconceptions primarily related with the misunderstanding of ‘voltage and electric field’, ‘ionic displacement and strain’, ‘thin film fabrication’, ‘energy transmission coefficient’, ‘thin film device designing’, ‘piezoelectric vibration damping’, ‘mechanical impedance matching’, ‘piezoelectric energy harvesting”, ‘resonance &amp; anti-resonance’, ‘best-selling devices’, and provides rectifications, aiming at their future progress.</p>

Origin of the abnormal reduction of the dielectric response for ReCOB crystals and its mechanism: theoretical and experimental exploration

The significant influence of ionic displacement polarization on distinct reduction in dielectric permittivity for LaCOB has been confirmed.

Thermal transients excite neurons through universal intramembrane mechano-electrical effects

Modern advances in neurotechnology rely on effectively harnessing physical tools and insights towards remote neural control, thereby creating major new scientific and therapeutic opportunities. Specifically, rapid temperature pulses were shown to increase membrane capacitance, causing capacitive currents that explain neural excitation, but the underlying biophysics is not well understood. Here, we show that an intramembrane thermal-mechanical effect wherein the phospholipid bilayer undergoes axial narrowing and lateral expansion accurately predicts a potentially universal thermal capacitance increase rate of ~0.3%/°C. This capacitance increase and concurrent changes in the surface charge related fields lead to predictable exciting ionic displacement currents. The new theory’s predictions provide an excellent agreement with multiple experimental results and indirect estimates of latent biophysical quantities. Our results further highlight the role of electro-mechanics in neural excitation; they may also help illuminate sub-threshold and novel physical cellular effects, and could potentially lead to advanced new methods for neural control.

Understanding the rate-dependent J–V hysteresis, slow time component, and aging in CH3NH3PbI3 perovskite solar cells: the role of a compensated electric field

Ionic displacement modifying the electric field in the device is found as most likely reason for the hysteresis which is examined by separating fast and slow processes and comparing devices with and without blocking layer.

Determination of Mobility and Charge Carriers Concentration from Ionic Conductivity in Sodium Germanate Glasses above and below Tg

The ionic conductivity and viscous flow data of xNa2O·(1−x)GeO2, 0.05<x<0.296, have been collected in a large temperature range, below and above their glass transition temperatures (Tg). A microscopic model is proposed, assuming that the ionic displacement would result from the migration of interstitial positively charged cationic pairs whose concentration is an activated function of temperature. Below Tg, their migration is also an activated mechanism, but a “free volume” would prevail above this temperature. This discontinuity in the migration mechanism justifies a Dienes-Macedo-Litovitz (DML) relationship to be representative of conductivity data above Tg and an Arrhenius law below. According to this model, the enthalpy deduced by the fit of high temperature data using a DML equation would correspond to the charge carrier formation, whose migration enthalpy, below Tg, could be deduced by the difference between the activation energy measured in the Arrhenius domain and the charge carrier formation enthalpy. To reduce the number of adjustable parameters numerical values were physically justified. We also applied a complete test for conductivity below Tg, using the so-called weak electrolyte model, splitting activation enthalpy EσA into formation and migration enthalpies and also explaining the variation of pre-exponential term of conductivity with composition.