  The high-pressure optical floating-zone method enables single crystal growth
of the Pmnb high-temperature phase of Li2FeSiO4. The influence of growth
conditions on crystal quality, phase homogeneity, and impurity formation in
Li2FeSiO4 is studied. The use of different starting materials, i.e., either the
P121/n1 or the Pmn21 polymorph, as well as optimization of various growth
conditions is investigated. Several mm3-sized high-quality single crystals are
obtained by the choice of the Pmn21 polymorph as the starting material. A
general challenge of Li2FeSiO4 crystal growth is polymorph control during
crystallization. While the temperature gradient at the solid-liquid interface
seems to have significant impact on stabilizing the Pmnb high-temperature
phase, growth velocity has no evident effect.
