Growth and preparation of LiZnP and LiZnAs for solid-state neutron detectors

Most gas-filled neutron detectors are difficult to manufacture as compact detectors. Boron-based compounds, such as BP, BN and BAs have shown limited success, and thus far do not appear promising due to problems with crystal growth and materials preparation. Although some Li compounds have been quite successful as neutron detectors, such as LiF thermoluminescent dosimeters and LiI scintillators, neutron detectors from Li-based semiconductor compounds have not been explored to a similar extent as B-based semiconductors. In the present study, crystals of the filled tetrahedral compound class (A^IB^IIC^V) of Li semiconductors were grown, known as Nowotny-Juza compounds, such as LiZnP and LiZnAs for investigation as high efficiency compact neutron detectors. Equimolar portions of Li, Zn and P or As were sealed under vacuum (10^-6 Torr) in quartz ampoules with a graphite lining. The loaded ampoules were placed into a compounding furnace and raised to 560°C to form the ternary compound, LiZnP or LiZnAs, and further annealed to promote crystallization. The synthesized compound was crushed into a fine powder and sealed in a tantalum ampoule by arc welding. The ampoule was mounted in a vacuum chamber with a background argon pressure of 300mTorr. The ampoule was connected to a low-voltage high-current power source where the LiZnP or LiZnAs was melted and slowly cooled to crystallization. The bulk crystals were extracted, then cut, and polished for further electrical and physical property investigations.