  One branch of the La-214 family of cuprate superconductors,
La1.6-xNd0.4SrxCuO4 (Nd-LSCO), has been of significant and sustained interest,
in large part because it displays the full complexity of the phase diagram for
canonical hole-doped, high Tc superconductivity, while also displaying
relatively low superconducting critical temperatures. The low superconducting
Tc's imply that experimentally accessible magnetic fields can suppress the
superconductivity to zero temperature. In particular, this has enabled various
transport and thermodynamic studies of the T = 0 ground state in Nd-LSCO, free
of superconductivity, across the critical doping p* = 0.23 where the pseudogap
phase ends. The strong dependence of its superconducting properties on its
crystal symmetry has itself motivated careful studies of the Nd-LSCO structural
phase diagram. This paper provides a systematic study and summary of the
materials preparation and characterization of both single crystal and
polycrystalline samples of Nd-LSCO. Single-phase polycrystalline samples with x
spanning the range from 0.01 to 0.40 have been synthesized, and large single
crystals of Nd-LSCO for select x across the region (0.07, 0.12, 0.17, 0.19,
0.225, 0.24, and 0.26) were grown by the optical floating zone method.
Systematic neutron and X-ray diffraction studies on these samples were
performed at both low and room temperatures, 10 K and 300 K, respectively.
These studies allowed us to follow the various structural phase transitions and
propose an updated structural phase diagram for Nd-LSCO. In particular, we
found that the low-temperature tetragonal (LTT) phase ends at a critical doping
pLTT = 0.255(5), clearly separated from p*.
