We manufacture LiNbO3 crystal lens professionally.
Basic Properties of optical LiNbO3 crystal lens as follow:
Crystal Structure:Trigonal, point group 3m
Lattice Parameters:a=b=5.148 , c=13.863  
Density:4.64 g/cm3 
Melting Point:1250 degrees
Curie Point:1142+/- degrees
Mohs Hardness:55
Dielectric Constant :e11/e0 = 85; e33/e0 = 29.5
Thermal Conductivity:38 W/m egrees at 25 egrees
Thermal Expansion Coefficient:a1=a2 =2x10-6 egrees, a3=2.2x10-6/ degrees at 25degrees
Piezoelectric Strain Constant:d22 = 2.04 x 10-11 C/N, d33 = 19.22 x 10-11 C/N
Elastic Stiffness Constant:CE11 = 2.04 x 1011 N/m2, CE33 = 2.46 x 1011 N/m2