Market leaders in temperature controlled microscopy, Linkam Scientific Instruments report on the use of the popular THMSG600 stage for birefringence research at the University of Silesia, Poland

Birefringence, a property of a crystalline material describes how within the material there are two distinct indices of refraction. This feature is associated with uniaxial crystals (hexagonal, tetragonal, and trigonal systems). This can be described as the optic axis running along the x-axis of the crystal and the o-wave perpendicular to the x-axis. Birefringent materials are used to create polarising filters or interference colours. Some familiar birefringent materials include tourmaline, calcite, quartz, ice, and barium titanate (BaTiO₃).

Krystian Roleder, the Regional Editor for the Central and Eastern Europe edition of the multinational journal "Phase Transitions" and Researcher at the Institute of Physics, University of Silesia has been studying birefringence measurements for a number of years. Mr Roleder has been using the THMSG600 stage to study birefringence in several materials, including BaTiO₃. He commented: This Linkam stage is indispensable for my scientific work."

In this research, Roleder and his colleagues have focused on the materials properties above crystallisation temperature, which has been little studied. BaTiO₃ is a popular crystal for scientists who wish to study birefringence properties, as it is freely available as large single quality crystals. Studied as a classic ferroelectric material, BaTiO₃ has been the focus of many research projects since its first recognition in the 1940s. Extensive studies have looked at the phase transitions and domain structure along with the optical, electrical and mechanical properties. The cubic to tetragonal phase change is described as the order-disorder type and is displacive in nature. It is widely accepted that the Ti ion becomes displaced from its position within the oxygen octahedron, and this is the cause of the polar region formation within the crystal. It is not fully understood why this displacement occurs. It was found that the BaTiO₃ crystals were birefringent over a broad temperature range but disappeared over 160-170°C.

The group has demonstrated the temperature dependence of the birefringence above crystallisation temperature and the behavior of anomalous birefringence can be attributed to the existence of polar clusters. These polar clusters originate due to the interdependence of the structural and polar soft modes. These polar clusters interrupt the cubic symmetry of the crystal and about crystallisation temperature the crystal become birefringent. These polar regions are connected to the movement of the Ti molecule within the oxygen cage.

Samples were tested using the THMSG600 stage on an Oxford Cryosystems Metripol Birefringence Imaging System and heated at a constant 0.2°C/min.

The THMS600 is one of the most widely used heating and freezing microscope stages on the market. With its excellent 0.1°C accuracy and stability, the THMS600 is used in many applications including birefringence research. The stage gives researchers the option to characterize their sample quickly by heating to

within a few degrees of the required temperature at a rate of up to 150°C/min with no overshoot. They may also modify the temperature ramp to a few tenths of a degree per minute so that they can closely examine the sample for any changes providing the ideal instrument for these studies.

Visit Linkam at www.linkam.co.uk and learn about the broad range of applications in the field of temperature-controlled microscopy.

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