Design Construction and Use of a Thermomechanical Detwinning Apparatus: Detwinning of Orthorhombic Nb2BaCu2O3

In this thesis I will describe a device designed and built for thermo- mechanically detwinning crystals. Twinning is a process in which a crys- talline structrure with two different axes of nearly equal length alternate directions throughout the material, effectively generating a single bulk material with two or more distinct internal crystals. This structure defect can lead to many other effects in the crystal, and it is useful to elimi- nate twinning in many materials in order to determine which properties are fundamental properties of the crystal, and which properties are ar- tifacts of the structural imperfections. The apparatus described in this thesis applies forces as large as 150 lbs along a single axis directions at temperatures as high as 650 C in a controlled gas environment. Under these conditions many crystals will align so the short axis of each unit cell aligns parallel to the axial pressure. This process reduces or eliminates twinning in many crystals leading to clearer interpretations of data from neutron scattering, and other experimental techniques. The initial results on NBCO are encouraging, although not ideal. The NBCO test sample is less twinned than originally, although the detwinning is not complete.