The state of a sample during crystal growth from high temperature solutions is not accessible in conventional furnace systems. An optimization of the growth parameters often requires arduous trial and error procedures in particular in case of novel multicomponent systems with unknown phase diagrams. Here we present a measurement technique based on lock-in amplification that allows for in-situ detection of the liquidus and solidus temperatures as well as structural phase transitions. A thin, metallic measurement wire is mounted in close vicinity to the melt. Characteristic anomalies in the time-dependent electrical resistivity of this wire allow for the detection of latent heat release without using a reference crucible. The method is implemented in a feedback furnace and enables an adjustment of the temperature profile based on the occurrence or absence of phase transitions. The absolute temperature serves as an additional source of information. Obtained phase transition temperatures are in good agreement with differential thermal analysis (DTA).
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