Structural and thermal properties of the monoclinic Lu2SiO5 single crystal: evaluation as a new laser matrix

The crystal structure of monoclinic Lu2SiO5 (LSO) crystals, grown by the Czochralski method, was determined at room temperature by X-ray diffraction. The unit-cell parameters are a = 10.2550 (2), b = 6.6465 (2), c = 12.3626 (4) A, β = 102.422 (1)° in space group I2/a. The linear thermal expansion tensor was determined along the a, b, c and c* directions over the temperature range from 303.15 to 768.15 K, and the principal coefficients of the thermal expansion tensor are found to be αI = −1.0235 × 10−6 K, αII = 4.9119 × 10−6 K and αIII = 10.1105 × 10−6 K. The temperature dependence of the cell volume and monoclinic angle were also evaluated. In addition, the specific heat and the thermal diffusivity were measured over the temperature ranges from 293.15 to 673.15 K and from 303.15 to 572.45 K, respectively. As a result, the anisotropic thermal conductivity could be calculated and is reported for the first time, to the best of the authors' knowledge. The specific heat capacity of LSO is 139.54 J mol−1 K−1, and the principal components of the thermal conductivity are kI = 2.26 W m−1 K−1, kII = 3.14 W m−1 K−1 and kII = 3.67 W m−1 K−1 at 303.15 K. A new structure model was proposed to better understand the relationships between the crystal structure and anisotropic thermal properties. In comparison with other laser matrix crystals, it is found that LSO possesses relatively large anisotropic thermal properties, and owing to its small heat capacity it has a moderate thermal conductivity, which is similar to those of the tungstates but lower than those of the vanadates.