Growth of binary organic NLO crystals: m.Na-p.NA and m.Na-CNA systems

• Published in: Materials letters 1994, Vol.20 (3), p.203-209
• Main Authors: Henningsen, T., Singh, N.B., Hopkins, R.H., Mazelsky, R., Hopkins, F.K., Frazier, D.O., Singh, O.P.
• Format: Article
• Language: English
• ISSN: 0167-577X; 1873-4979
• DOI: 10.1016/0167-577X(94)90088-4

Experiments were carried out to grow 3-nitroaniline (m.NA) crystals doped with 4-nitroaniline (p.NA) and 2-chloro 4-nitroaniline (CNA). The measured undercooling for m.NA, p.NA, and CNA were 0.21, 0.23 and 0.35 t m K respectively, where t m represents the melting temperature of the pure component. Because of the crystals' large heat of fusion and large undercooling, it was not possible to grow good quality crystals with low thermal gradients. In the conventional two-zone Bridgman furnace, the temperature of the hot zone had to be raised above the decomposition temperature of CNA, p.NA and m.NA to achieve the desired thermal gradient. To avoid decomposition, an unconventional Bridgman furnace was used. Two immiscible liquids, silicone oil and ethylene glycol, were used to build a special two-zone Bridgman furnace. A temperature gradient of 18 K/cm was achieved without exceeding the decomposition temperature of the crystal. The binary crystals, m.NA-p.NA and m.NA-CNA, were grown in centimeter sizes in this furnace. X-ray and optical characterization showed good optical quality.