Fig. 4: Heat diffusion model.
a–c Schematic description of the 2-dimensional model system. a Experimental geometry showing the laser pump pulse incident normally on the Ti3O5 pellet and X-ray probe at a grazing incidence. b A section of the Ti3O5 pellet is represented with a simulation box of 500 × 500 nodes of which 400 nodes below the surface are photoexcited. In this scale, the X-ray probed depth is about 80 nodes and laser penetration depth is 10 nodes. c A zoomed image on the photoexcited region of the system shows the 2-dimensional grid of ”nodes”. Several nodes together form crystallite/grain (for example, the ith and jth grains) and are separated by grain boundaries. Three different thermal exchange coefficients between the nodes are represented by the green, orange and purple arrows for respectively the intragrain coefficient(ci,i), intergrain coefficient(ci,j) and the heat exchange coefficient(ci,air) with the surrounding air across the sample surface. d, e The initial spatial distribution of the λ-phase domains within the X-ray probed regime for d S = 100 × 100 nm2 and e S = 500 × 500 nm2 crystallite sizes. The grain boundaries are denoted with the dashed lines. Random number of assymetric λ-phase domains are distributed within each grain.
