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A ferroelectric phase transition under an external bias electric field after field cooling and zero field cooling in barium titanate single crystals shows scale invariant nucleation and growth of complex domain structures. The avalanche energy exponents vary with the external bias, depending on the cooling history of the sample under applied field or zero field cooling. After field cooling, resulting in a single domain sample, the energy exponent is near the integrated mean field value of 5/3, namely, 1.68 ± 0.022. The sample after field cooling shows the same exponent with an external bias electric field range of up to 4.5 kV/cm. The exponent of a multi-domain sample, after zero field cooling, decreases from ε = 1.85 to the fixed point of 1.66 under high fields. The different behavior is attributed to the greater complexity of domain patterns in the multi-domain sample, which reduces to a single domain state under strong applied fields. Compared with the single-domain state, the multi-domain state has more domain boundaries and the intersections formed by these domain boundaries. These domain boundaries and their intersections will hinder the movement of the phase boundary and act as a pinning effect on the front of the phase interface. The effect is to generate more small energy signals, making the critical exponent high. At the same time, the aftershock time distribution (Omori law) remains the same for all switching conditions with an Omori exponent near −1 and switching time correlations of −1 ± 0.05 for short times (<1 s) and −2 ± 0.10 for long times (>1 s). [ABSTRACT FROM AUTHOR]

Ferroic phase transformation in monolayer nanosheets or nanoribbons endows 2D nanoelectronic devices with novel functionalities. However, less is known how the phase transformation behaves with the system size. Combined with molecular dynamic simulations and a machine learning model, we systematically investigate the temperature induced ferroic phase transformation in monolayer GeSe nanoribbons, which exhibits remarkable size effect. Specifically, the transformation hysteresis is found continuously decreased with ribbon width at the investigated scales. In contrast, the transformation temperature of monolayer GeSe nanoribbons shows non-monotonic size-dependency, i.e., it is first increased and then decreased as we narrow the GeSe nanoribbons. We attribute this to a competition between the enhanced ripple deformation, which will promote phase transformation upon cooling, and the stronger edge effect that can suppress phase transformation. In addition, the two factors are well captured by the Landau model, which will deepen our understanding of phase transformation behaviors in 2D ferroic materials. [ABSTRACT FROM AUTHOR]

The motion of phase fronts during a ferroelectric phase transition is intermittent and follows avalanche dynamics. In the present study, we show that an intermittent propagation mode generates spikes of depolarization currents at an extremely slow heating rate of 0.05 K/min in BaTiO3 (BTO) and 0.7Pb(Mg2∕3Nb1∕3)O3-0.3PbTiO3 (PMN-PT) single crystals. Such "jerks" are indicative of avalanche dynamics, and their energy exhibits a power law distribution with exponents of ε = 1.3 ± 0.10 and ε = 1.5 ± 0.10 for BTO and PMN-PT, respectively. The rate of aftershocks after big events decays as an Omori-like power-law and interevent times are characterized by a universal double power-law distribution, indicating the critical temporal correlations between the avalanche events. [ABSTRACT FROM AUTHOR]

It is well known that martensite aging effects in shape memory alloys can be simply removed when the aged martensite experiences a reverse transformation to the parent phase followed by cooling back to the martensite state. This 'deaging' process has been known to be very fast but it remains a question as to whether there exists a short-time limit for such a fast deaging process. In this letter, we report that there indeed exists a short-time limit for the deaging. We have studied the aging and deaging of a Au-49.5Cd shape memory alloy, and found that complete removal of the previous aging, as manifested by the recovery of martensite transition start temperature (Ms), occurs only after aging in the parent phase for more than 500 s. Shorter time holding/aging in the parent phase results in a higher Ms as compared with the fully deaged case. Therefore, there is a fast relaxation process during the deaging or parent phase aging process. Atomistic simulations suggest that the origin of the observed time-dependent deaging arises from the change in short-range configurations of point defects, being the same as that of the martensite aging. As a result, it is possible to unify the microscopic mechanism of aging in both martensite and parent phase; both are due to a symmetry-conforming short-range ordering tendency of point defects. [ABSTRACT FROM AUTHOR]