Detailed kinetic measurements show that growth rate in dependence on temperature is characterized by strongly nonmonotonous changes. Such phenomenon is known as “kinetic anomalies”. Kinetic anomalies investigation of mixed crystal growth showed that their chemical composition also changes nonmonotonically with temperature. It was assumed that such nonmonotonic changes of chemical composition will result in zone formation in bulk of crystal.

            Sodium chlorate-bromate system was chosen for experiments since kinetic data and impurity (sodium bromate) concentration are known in dependence on temperature. Crystals for investigation have been received by three different methods. The first one (combined method) is combination of temperature gradient and temperature decrease methods. Other two is spontaneous crystallization and constant supercooling method (microcrystallization). Last two of them were used for comparison of chemical composition distribution at crystals grown in different conditions from solution with the same composition.

            Received crystals were investigated by two methods: optical microscopy and x-ray microtomography.

            Crystals grown by combined method show zone distribution of interference colors. At the same time crystals grown by other methods have a domain or homogeneous distribution of interference colors. It means that tensions also as compounds distribution are different and show zone character only for crystals grown by combined method.

            Microtomography investigation shows that crystals grown by combined method have zone distribution of grayscale index. Grown crystals have from one to three zones enriched by bromate compound in dependence on temperature range and amount of anomaly extremes located in this range. External zone has maximum intensity on grayscale index profile in every case where is more than one zone. It doesn’t match to intensity of anomaly peaks and theoretical concentration of bromate. We link it to the features of X-Ray microtomography and reconstruction method where external zone “shields” internal zones.

            Received data show that chemical composition can change nonmonotonic even in case of monotonic temperature decrease at growth process due to kinetic anomalies influence. This conclusion is supported by X-Ray microtomography data as well as data received by optical microscopy. There are some problems with investigations of our materials by x-ray microtomography method. Main of them is low contrast of received zonality. It results in additional treatment of microtomography slices and grayscale index profiles. Other one is higher intensity of external zone in comparison with theoretical prediction. Both of these problems might be solved with involvement equipment with higher energy tube.

            The reported study was partially supported by Russian Foundation for Basic Research, research project No. 12-05-00876-а.

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1. Quantitative analysis of morphology of polycrystalline precipitate received in temperature ranges of growth rate anomalies
2. Kinetic anomalies of mixed crystals growth