The extinction coefficient at 3500 cm-1 (α3500) near the maximum of the broad background absorption band in the spectrum of a-quartz is proportional to the H-bonded OH content. At this frequency and at a crystal temperature of ~300°K, infrared measurements were made on several thin F-cut samples. In each case, the radiation beam was parallel to γ[10.0] and the sample was translated across the beam in the Z direction [00.1], The resulting maps of the variations of α3500 show that the H-bonded OH content of the cultured material is not related to that of the seed. Each α3500 topograph is fairly symmetrical about the parallel to the X-axis centerline implying a relationship between H-bonded OH content and growth rate. In one sample, the growth rate was purposely accelerated at about the halfway point. This change in growth rate caused an increase in α3500 (H-bonded OH content).
Synthetic crystalline α-quartz often exhibits lamellar inhomogeneities or striations which, in the Z-growth region, are approximately parallel to the (00.1) plane. Comparisons of α3500 topographs with Schlieren photographs of untreated and heat-treated samples and with Twyman-Green interferograms for the same set of specimens indicate the following:
(1) Changes in growth rate cause striations.
(2) Milky layers (inclusions of ordered water), seen in some samples after prolonged heat treatment at T ≥ 500°C, develop in regions of originally higher assoo (H-bonded OH content) which are also those of initially lower refractive index.
(3) There is a one to one correspondence between the α3500 (H-bonded OH content) variations, the striation boundaries, and the refractive index gradients.