The growth of ruby (Al2O3:Cr) crystals from PbF2-B2O3 flux is reported
. The crystal growth was conducted by heating a mixture of solute and
flux at 1100 degrees C for 10 h, followed by cooling to 500 degrees C
at a rate of 5, 10, 20 or 40 degrees C h(-1). Red and transparent ruby
crystals were obtained. A combination of slow cooling with evaporatio
n of the flux produced crystals of ruby. The simple PbF2 flux gave rub
y crystals of up to 12 mm x 9 mm x 1 mm in size. The crystal sizes dec
reased with increasing rate of cooling. The evaporation loss and cryst
al size decreased with increasing amount of B2O3 added to PbF2. The Pb
F2-B2O3 flux produced a lot of small ruby crystals. Inclusions were ra
rely found in the ruby crystals. The form of the ruby crystals was a h
exagonal thin plate bounded by c{0001}, r{10 (1) over bar 1} and d{01
(1) over bar 2} faces. On the basis of microscopic observation, the ce
ntral parts of c faces were slightly swollen. The growth hillocks were
observed on the c faces of crystals. The step heights of the hillocks
were in the region of 0.2-15 mu m. The chromium was incorporated pref
erentially in the center parts of crystals. The refractive index of tr
ansparent ruby crystals was 1.73+/-0.01.