Tuning Coherent-Phonon Heat Transport in LaCoO/SrTiO Superlattices.

Accessing the regime of coherent phonon propagation in nanostructures opens enormous possibilities to control the thermal conductivity in energy harvesting devices, phononic circuits, etc. In this paper we show that coherent phonons contribute substantially to the thermal conductivity of LaCoO/SrTiO oxide superlattices, up to room temperature. We show that their contribution can be tuned through small variations of the superlattice periodicity, without changing the total superlattice thickness.

Deconvolution of Phonon Scattering by Ferroelectric Domain Walls and Point Defects in a PbTiO Thin Film Deposited in a Composition-Spread Geometry.

We present a detailed analysis of the temperature dependence of the thermal conductivity of a ferroelectric PbTiO thin film deposited in a composition-spread geometry enabling a continuous range of compositions from ∼25% titanium deficient to ∼20% titanium rich to be studied. By fitting the experimental results to the Debye model we deconvolute and quantify the two main phonon-scattering sources in the system: ferroelectric domain walls (DWs) and point defects. Our results prove that ferroelectric DWs are the main agent limiting the thermal conductivity in this system, not only in the stoichiometric region of the thin film ([Pb]/[Ti] ≈ 1) but also when the concentration of the cation point defects is significant (up to ∼15%).

Relaxation Mechanisms and Strain-Controlled Oxygen Vacancies in Epitaxial SrMnO Films.

SrMnO has a rich epitaxial strain-dependent ferroic phase diagram, in which a variety of magnetic orderings, even ferroelectricity, and thus multiferroicity, are accessible by gradually modifying the strain. Different relaxation processes, though, including the presence of strain-induced oxygen vacancies, can severely curtail the possibility of stabilizing these ferroic phases. Here, we report on a thorough investigation of the strain relaxation mechanisms in SrMnO films grown on several substrates imposing varying degrees of strain from slightly compressive (-0.

The exit-wave power-cepstrum transform for scanning nanobeam electron diffraction: robust strain mapping at subnanometer resolution and subpicometer precision.

Scanning nanobeam electron diffraction (NBED) with fast pixelated detectors is a valuable technique for rapid, spatially resolved mapping of lattice structure over a wide range of length scales. However, intensity variations caused by dynamical diffraction and sample mistilts can hinder the measurement of diffracted disk centers as necessary for quantification. Robust data processing techniques are needed to provide accurate and precise measurements for complex samples and non-ideal conditions.