YbAl3(BO3)4 crystal of good optical quality was grown by the flux method. The structure of YbAl3(BO3)4 crystal was determined by single-crystal X-ray diffraction. The experiment shows that YbAl3(BO3)4 belongs to the double bo-rates with a trigonal structure. The space group is R32 and its unit cell constants were measured to be a = 0.92965 nm, c=0.72129 nm, V = 0.53673 nm3, Z=3. The transmittance spectra were measured. The cut-off of YbAl3(BO3)4 crystal is 216 nm, and there are two absorption peaks located at 940 and 975 nm from 190 nm to 2600 nm. The thermal properties of YbAl3(BO3)4 crystal were studied for the first time. The average thermal expansion coefficients were determined to be 2×10-6/℃, 9.5×10-6/℃along a- and c- direction. The specific heat of YbAl3(BO3)4 crystal was measured to be 0.6695 J·(g·℃) -1 at room temperature . All results indicate that the YbAl3(BO3)4 crystal is an excellent stoichioimet-ric laser material.
