  We present the design and construction of an apparatus that measures the
Seebeck coefficient of single crystals under in-situ tunable strain at
cryogenic temperatures. A home-built three piezostack apparatus applies
uni-axial stress to a single crystalline sample and modulates anisotropic
strain up to 0.7%. An alternating heater system and cernox sensor thermometry
measures the Seebeck coefficient along the uniaxial stress direction. To
demonstrate the efficacy of this apparatus, we applied uniaxial stress to
detwin single crystals of BaFe2As2 in the orthorhombic phase. The obtained
Seebeck coefficient anisotropy is in good agreement with previous measurements
using a mechanical clamp.
