Thermal properties of monoclinic crystal Er3+:Yb3+:Ca4YO(BO3)3

A large Er3+–Yb3+ co-doped yttrium calcium oxoborate [Er3+:Yb3+:Ca4YO(BO3)3, abbreviated as Er:Yb:YCOB] single crystal, with dimensions of 2.5 cm in diameter and 9.0 cm in length, has been grown along the crystallographic b axis by the Czochralski method. X-ray powder diffraction results show that the as-grown Er:Yb:YCOB crystal belongs to the monoclinic system with space group Cm; the unit-cell constants are a = 8.085, b = 16.048, c = 3.528 A and β = 101.11°. The high crystalline quality of the as-grown single crystal was confirmed by high-resolution X-ray diffraction, which showed the full width at half-maximum of the rocking curves to be less than 20 arcseconds on the (060) and (\overline 201) diffraction planes. The measurement and calculation of the symmetrical second-rank tensor for the monoclinic crystal are described in detail in this paper. The principal coefficients of thermal expansion of the as-grown Er:Yb:YCOB crystal are αI = 11.95 × 10−6 K−1, αII = 9.20 × 10−6 K−1 and αIII = 18.93 × 10−6 K−1 over the temperature range 303.15–873.15 K. The specific heat of the crystal is 725.6 J kg−1 K−1 at 328.15 K. The principal thermal conductivity parameters are KI = 2.882 W m−1 K−1, KII = 2.687 W m−1 K−1 and KIII = 2.692 W m−1 K−1 at 328.15 K.