Self-organizing formation of dendrite domain structures in lithium niobate and lithium tantalate crystals

Thermo-solutal and kinetic modes of stable dendritic growth with different symmetries of crystalline anisotropy in the presence of convection

“…-investigations of the joint influence of a tiny amount of impurity and convective transport on the growth kinetics (which is important for a description of dendritic crystals growing under terrestrial and microgravity conditions [6][7][8]); -numerical simulations of solidification, taking account of the anisotropic properties of moving crystal-liquid interfaces and convective boundary conditions (which is important to check the differences in the selection criteria at small and large values of growth Péclet numbers [29,30]); -computational modelling of intensive (even turbulent) flow in the liquid core of a solidifying sample, which provides convective transport (5.1) and (5.2) at the dendrite surface (this is important to check the 'convective' criterion (5.13)); -checking the transition from the diffusion-limited (solutally and thermally controlled) regime to the kinetically limited regime (which is important to verify theories that predict a smooth/sharp change of the dendrite velocity with the exchange of preferred crystallographic growth direction [12,32,43]); -direct measurements of the velocity of convective flow prior to and during solidification of levitating droplets [69] (this may provide an input of the flow velocity as a measurable parameter into the models with convection as discussed in Galenko et al [36]); -a comparison of stitching solutions [32] (working in a wide range of undercooling) with exact solutions [94][95][96] or asymptotic solutions [97] (which provide an analytical description for a narrow range of undercooling); and -a comparison with experimental and computational data on two-dimensional dendrites with sixfold symmetry (which is important for the description of dendritic patterns appearing in ferroelectric materials under electric fields [98]).…”

The boundary integral theory for slow and rapid curved solid/liquid interfaces propagating into binary systems

“…A number of experimental data show that in many cases the growing shapes of dendrites are nonsymmetric. For instance, ice crystals evolving in pure water and in water-ethyleneglycol solution or dendritic evolution in aluminium nitride, lithium niobate or lithium tantalate represent several examples of the sixfold symmetry which is caused by the hexagonal crystalline anisotropy [4,5,[74][75][76][77][78]. In these cases, dendritic shapes do not satisfy the Ivantsov solutions [70,71] and one must use the Horvay-Cahn solutions characterizing possible lower symmetric dendritic shapes [79][80][81].…”

Investigation of AFM-based machining of ferroelectric thin films at the nanoscale

“…In ferroelectric samples, tomography investigations have typically been achieved by carefully polishing relaxor ferroelectric ceramic samples, 35 repeated surface chemical etching of bulk Pb(Zr,Ti)O 3 , 36 or via non-destructive confocal Raman microscopy of both periodically poled as well as more complex dendritic electrically-induced domains in LiNbO 3 . 37,38 In this context, AFM-based machining provides an alternative low-cost option to both fabricate nanostructures as well as undertake tomographic functional investigations, while avoiding problems related to ion-injection from FIB, 39 mask limitations (where the nanostructure is limited by the shape and dimensions of the mask) with mask-assisted bottom-up approaches 14 and low resolution (~ 1 µm) of confocal Raman microscopy. 18 The AFM setup also enables data to be collected in-situ during the machining process, thereby providing insight into the mechanical as well as functional properties, such as the conductivity, of the material.…”