Scale-invariant avalanche dynamics in the temperature-driven martensitic transition of a Cu-Al-Be single crystal

We have combined high sensitivity, extra-low differential temperature scanning rate calorimetry, and acoustic emission (AE) measurements to study avalanches during the cubic ↔ 18R martensitic transition of a Cu-Al-Be single crystalline shape memory alloy. Both AE and calorimetry corroborate a good power-law behavior for cooling with an exponent ε 1.6. For heating, a slope is observed in the maximum likelihood curves, which confirms that our data are affected by an exponential cutoff. An effective energy exponent, ε ∼ 1.85, and a cutoff, λ −1 = 0.115(38)E-3 aJ, were determined by fits of power-laws with exponential damping. The long tail observed in the low-temperature region by calorimetric measurements suggests the existence of significant elastic effects that constrain the progress of the transformation at low temperatures. While thermodynamic features such as transformation enthalpy and entropy are those expected for Cu-based shape-memory alloys undergoing a cubic ↔ 18R transition, the critical behavior deviates from the corresponding behavior expected from this symmetry change. These deviations are a consequence of the elastic hardening induced by the interplay of the transformation with dislocation jamming, which has the effect of effectively reducing the number of pathways connecting the parent and martensitic phaseMinisterio de Ciencia,Innovación y Universidades (MAT2016-75823-R)Engineering and Physical Sciences Research Council (EP/P024904/1

Dynamic heat flux experiments in Cu67.64Zn 16.71Al15.65: Separating the time scales of fast and ultra-slow kinetic processes in martensitic transformations

Crackling noise and avalanches during the martensite phase transformation of Cu67.64Zn16.71Al15.65 were investigated. Heat flux measurements with extremely slow heating rates of 0.005 Kh -1 allowed sufficient separation between the continuous background and the avalanche jerks. The jerk enthalpy is below 3 of the total transformation enthalpy. The crackling noise follows power law behavior with an energy exponent near ε=1.8. The jerks are almost uncorrelated with approximately a Poisson distribution of the waiting times between jerks. Quantitative analysis showed a scaling behavior with p(wt) ∼ wt (γ-1)exp(-wt/τ)n with γ=0.7 and n ≈ 1.Ministerio de Educación y Ciencia FIS2006-0404

A Theory of Ferroelectric Phase Transition in SrTiO3_3 induced by Isotope Replacement

A theory to describe the dielectric anomalies and the ferroelectric phase transition induced by oxygen isotope replacement in SrTiO$_3$ is developed. The proposed model gives consistent explanation between apparently contradictory experimental results on macroscopic dielectric measurements versus microscopic lattice dynamical measurements by neutron scattering studies. The essential feature is described by a 3-state quantum order-disorder system characterizing the degenerated excited states in addition to the ground state of TiO$_6$ cluster. The effect of isotope replacement is taken into account through the tunneling frequency between the excited states. The dielectric properties are analyzed by the mean field approximation (MFA), which gives qualitative agreements with experimental results throughout full range of the isotope concentration.The phase diagram in the temperature-tunneling frequencycoordinate is studied by a QMC method to confirm the qualitative validity of the MFA analysis.Comment: 26 pages, 8 figure

Chirality and Symmetry Breaking in a discrete internal Space

In previous papers the permutation group S_4 has been suggested as an ordering scheme for elementary particles, and the appearance of this finite symmetry group was taken as indication for the existence of a discrete inner symmetry space underlying elementary particle interactions. Here it is pointed out that a more suitable choice than the tetrahedral group S_4 is the pyritohedral group A_4 x Z_2 because its vibrational spectrum exhibits exactly the mass multiplet structure of the 3 fermion generations. Furthermore it is noted that the same structure can also be obtained from a primordial symmetry breaking S_4 --> A_4. Since A_4 is a chiral group, while S_4 is achiral, an argument can be given why the chirality of the inner pyritohedral symmetry leads to parity violation of the weak interactions.Comment: 42 pages, 3 table

Dynamic heat flux experiments in Cu67.64Zn 16.71Al15.65: Separating the time scales of fast and ultra-slow kinetic processes in martensitic transformations

Crackling noise and avalanches during the martensite phase transformation of Cu67.64Zn16.71Al15.65 were investigated. Heat flux measurements with extremely slow heating rates of 0.005 Kh -1 allowed sufficient separation between the continuous background and the avalanche jerks. The jerk enthalpy is below 3 of the total transformation enthalpy. The crackling noise follows power law behavior with an energy exponent near ε=1.8. The jerks are almost uncorrelated with approximately a Poisson distribution of the waiting times between jerks. Quantitative analysis showed a scaling behavior with p(wt) ∿ wt (γ-1)exp(-wt/Ï„)n with γ=0.7 and n ≈ 1. © 2011 American Institute of Physics.The calorimetric experiments have been supported in Seville by Project FIS2006-04045. J. Manchado wishes to thank to Fundacio´n Ca´mara for a research grant. We want to thank also to Dr. A. Planes for supplying the sample.Peer Reviewe

LaAlO3: A substrate material with unusual ferroelastic propeties

[eng] Twin boundary dynamics in LaAlO3 is associated with non-linear anelasticity. Ultrasonic studies of non-linear twin boundary dynamics between 80 and 520 K show that cooling substrates from temperatures near the ferroelastic transition at 813 K generate three characteristic thermal regimes with different non-linear dynamics. Twin boundaries are initially highly mobile. Anelastic strain amplitudes versus stress are power law distributed with an exponent of 2.5. No de-pinning was found down to elastic strain amplitudes of ε0 ∼ 10−7. The power law is gradually replaced between 370 K and 280 K by few large singularities (jerks) due to massive rearrangements of the domain structure for ε0 larger than ca. 5 × 10−5. At lower temperatures, the domain structure is pinned with well-defined thresholds for de-pinning. The de-pinning is not accompanied by global rearrangements of twin patterns below room temperature. Unexpectedly, the low-temperature critical de-pinning strain amplitude decreases with decreasing temperature, which may indicate an additional, so far unknown phase transition near 40 K

Twin walls in anorthoclase are enriched in alkali and depleted in Ca and Al

Composition profiles have been measured in transformation twin walls of the albite type in anorthoclase. Regions close to the walls between two twin domains are enriched in K and Na and depleted in Ca and Al. Microanalysis experiments show high mobility of alkali cations close to twin boundaries. Twin walls are generated via the displacive phase transition C2/m-C1\u304 in Al, Si disordered feldspar, and the chemical heterogeneity is a fingerprint for the subsequent diffusion of alkali and earth alkali ions during the cooling history of the sample