Quantifying antisite defect concentrations in yttrium aluminum garnet by high-precision density analysis

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Quantifying the nature and density of lattice defects in high-quality crystals is often difficult or impossible with commonly employed material characterization techniques. In many cases, even the density of intentionally doped impurities present in a grown crystal must be inferred indirectly using methods such as mapping spatial variations in crystal properties or, when the defects are optically active, interpreting optical absorption with imprecisely known oscillator strengths. In this work we explore gravimetric techniques to obtain absolute defect densities in crystals, a powerful approach often overlooked in modern materials science. A hydrostatic weighing apparatus based on Archimedes’ principle was constructed, tested, and refined to enable high-precision density measurements of small crystal samples. Application of this system is illustrated by determining the density of Yttrium Aluminum Garnet (YAG) relative to a high-purity silicon crystal density reference, minimizing traditional difficulties in correcting for the variations in surface tension and the water and air density due to small changes in ambient temperature, pressure, and solution composition. This method, using a relatively simple apparatus and small samples, is effective in measuring the intrinsic concentration of Y–Al antisite lattice defects in YAG, agreeing with results from far more elaborate high-resolution optical laser spectroscopy at cryogenic temperatures. Furthermore, we quantitatively analyze the effects of several potential sources for error, including natural variations in isotope distributions, residual surface contamination, and ambient temperature or pressure variations. Subsequently, we find that the density analysis method is a promising technique for characterizing new and modified materials being developed for applications ranging from solid-state lasers and scintillators to quantum information.