416 Stella Pedrazzini et al.


(Bunton et al., 2007; La Fontaine et al., 2015) and was deemed to be one of the key variables requiring optimization in this work. One sample was therefore used for a calibration experiment, in which the laser energy was systematically changed over a range 0.05–0.6nJ/pulse, with at least 600,000 ions captured at every setting, with the evaporation rate maintained at 0.7%. To ensure consistency, the starting point and finishing point of the experiment were both 0.4 nJ. Analysis of the data sets was performed in part using the standard Cameca Integrated Visualization and Analysis


ab


Software (IVAS) 3.6.6 software and partly by converting the data files to the IVAS extended position file (epos) format, which provides additional outputs characterizing each reconstructed ion, including instantaneous voltage, recon- structed x, y, and z coordinates, time of flight, and whether an ion is detected as a single event or was one of multiple detected ions triggered by the same laser pulse. Matlab (Mathworks) and C+ + scripts custom-written for the present analysis were used to read the outputs, to perform background corrections, to read the number of multiple hits at each laser energy, to analyze the effect of different range widths on chemical composition and to plot multiple hit correlation histograms.


RESULTS


____ 4µm


c


-2.00 -1.50 -1.00 -0.50 0.00 0.50


60 70 80 90 100 110


Temperature (K) ZFC 1000 Oe


Figure 1. a: Schematic drawing of the yttrium barium copper oxide unit cell, (b) secondary electron micrograph showing the distribution of Y-211 particles (darker) within the Y-123 single grain matrix, as viewed along the <a> axis, (c) superconductivity measurements showing a sharp transition at 90 K, typical of the fully oxygenated perovskite.


ab Y-123 10 nm Y-211 Y Ba Cu O


10 20 30 40 50 60


0 0 5


The TSMG process produced a microstructure consisting of discrete Y-211 particles <5 μm in diameter within the single crystal Y-123 matrix, as shown in a typical SEM micrograph in Figure 1b. SQUID magnetization measurements, on a 3mm diameter sample of the analyzed material, showed a sharp decrease in magnetization signal at 90 K, confirming that the superconducting Y-123 phase is fully oxygenated. The fact that these melt-grown crystals have excellent superconducting properties (as shown in Fig. 1c) provides confidence in their chemical composition. It is possible, though unlikely, that the sample composition as measured by APT could have been affected by the FIB-based specimen preparation procedure. Hence, low-voltage final-stage mil- ling was performed in the FIB to minimize the Ga-affected volume and a separate initial data set was collected from the same sample until Ga contamination was no longer detect- able by APT. Data from an APT sample containing an Y-211 particle


is shown in Figure 2a, allowing the interface between Y-211 and the surrounding Y-123 matrix to be analyzed. Y-211 particles are electrical insulators, which makes them more likely to fracture when subjected to the electric fields


Cu Ba O Y


10


15 Distance (nm)


Figure 2. a: Reconstruction of a sample containing a Y-211/Y-123 interface and (b) one-dimensional concentration profile along the z axis of the sample. Iso-concentration surface shown at 15 at% Y highlights the position of the interface.


20


25


Magnetisation (emu)


Concentration (at%)


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