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A New Kösters Prism Interferometer for Simultaneous Determination of Refractive Index and Thermal Expansion of Crystals as a Function of Temperature
Author(s) -
Womersley M. N.,
Thomas P. A.
Publication year - 1996
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889896006590
Subject(s) - orthorhombic crystal system , phase transition , ferroelectricity , refractive index , thermal expansion , prism , crystal (programming language) , dielectric , condensed matter physics , phase (matter) , optics , interferometry , atmospheric temperature range , transition temperature , materials science , chemistry , crystal structure , crystallography , physics , thermodynamics , optoelectronics , computer science , metallurgy , programming language , superconductivity , organic chemistry
An uniquely-modified Kosters prism interferometer for the simultaneous and independent measurement of refractive index, δn(T), and thermal expansion, δl(T), as a function of temperature in the range 308-1273 K, is described. The capabilities of the system are demonstrated via measurement of δn(T) and δl(T) along both the [100] and [001] directions up to and through the α-8 phase transition in quartz, with results in good agreement with previous measurements. Further to this, experiments to determine δn(T) and δn(T) along the [100], [010] and [001] directions in the orthorhombic nonlinear optical crystal indium-doped KTiOAsO 4 are described. The results are used to show that the ferroelectric-paralectric phase transition at T c =1063 K is second-order and exhibits Landau-type behaviour over a range of 100 K below T c . Finally, similar experiments on the orthorhombic crystal Ba 2 NaNb 5 O 15 are reported. The behaviours of δn(T) and δl(T) at the ferroelastic phase transition at 563 K and the ferroelectric-paraelectric phase transition at T c = 849 K are discussed. Clear evidence of the existence of polar fluctuations in the paraelectric phase is presented.