In situ temperature profile measurements with high-energy X-rays as a probe of optical floating zone crystal growth environment

Abstract

The ability of optical floating zone (OFZ) furnaces to rapidly produce large single crystals of complex emerging materials has had a transformative effect on many scientific fields that require samples of this type. However, the crystal growth process within the OFZ furnace is not well understood owing to the challenges involved in monitoring the high-temperature crystal growth process. Novel beamline-compatible optical furnaces that approximate the inhomogeneous growth environment within an OFZ furnace have been fabricated and tested in high-energy synchrotron beamlines. It is demonstrated that temperature profiles can be effectively extracted from powder diffraction data collected on polycrystalline ceramic rods heated at their tip. Furthermore, these measured temperature profiles can be accurately reproduced using a heat-transfer model that accounts for solid-state thermal conduction, partial sample lamp power absorption, convective air cooling and radiative cooling, allowing key thermal parameters such as thermal conductivity to be extracted from experimental data.

Toward In Situ Synchrotron Mapping of Crystal Selection Processes during Crystal Growth

“…However, the success of this approach suggests that it can be adapted in the future to study OFZ crystal growth in situ once a synchrotron-compatible furnace is available, something that is the target of our broader research efforts within the GENESIS EFRC. 15 Tracking Granularity. The main sample studied in this work is boule A, a TiO 2 sample that was obtained from the seed rod of an OFZ crystal growth experiment shown in Figure 1a.…”

“…This means that the sample temperature profile is generally unknown, a challenge that we have recently begun to address through in situ synchrotron studies discussed elsewhere. 15 Additionally, the shape of the solid−liquid interface is unknown during the growth since this interface is buried and cannot be visually resolved. While the postmortem analysis of crystal growth boules suggests that the shape of the solid−liquid interface has an important effect on growth outcomes, 16 good nondestructive characterization tools suitable for following the crystal selection process in situ are not presently available, and their development is the main focus of this work.…”

“…Instead, there are typically a multitude of homogeneous nucleation sites on the polycrystalline seed rod, as has been schematically illustrated elsewhere. 15 As a result, crystal selection occurs during the initial portion of the growth during which faster-growing grains in the crystal growth boule crowd out and terminate the growth of grains that have less optimal growth orientations. After a few centimeters of growth, the crystal selection process is typically complete with the growth stabilizing only one or two dominant grains.…”

“…In general, OFZ crystal growth is only monitored optically using a video camera installed for this purpose. This means that the sample temperature profile is generally unknown, a challenge that we have recently begun to address through in situ synchrotron studies discussed elsewhere . Additionally, the shape of the solid–liquid interface is unknown during the growth since this interface is buried and cannot be visually resolved.…”

“…During OFZ crystal growth, experimental constraints generally prevent growths from starting at a single nucleation site (though seed crystals are occasionally used; they are difficult to mount in a precisely controlled orientation and can easily be destroyed if there are problems during the initiation of the growth). Instead, there are typically a multitude of homogeneous nucleation sites on the polycrystalline seed rod, as has been schematically illustrated elsewhere . As a result, crystal selection occurs during the initial portion of the growth during which faster-growing grains in the crystal growth boule crowd out and terminate the growth of grains that have less optimal growth orientations.…”