| Summary: | The travelling solvent floating zone (TSFZ) growth of Eu-substituted LSCO (La<sub>1.81−x</sub>Eu<sub>x</sub>Sr<sub>0.19</sub>CuO<sub>4</sub>, with nominal x = 0 ÷ 0.4) single crystals was systematically explored for the first time. The substitution of La with Eu considerably decreased the decomposition temperature. Optimal growth parameters were found to be: oxygen pressure 9.0–9.5 bars; Eu-free CuO-poor solvent (66 mol% CuO) with a molar ratio of La<sub>2</sub>O<sub>3</sub>:SrCO<sub>3</sub>:CuO = 4:4.5:16.5 and growth rate 0.6 mm/hour. The obtained single crystals were characterized with optical polarized microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy analysis. The solubility of Eu in LSCO appeared to be limited to x~0.36–0.38 under the used conditions. The substitution of La<sup>3+</sup> with smaller Eu<sup>3+</sup> ions led to a structural transition from tetragonal with space group <i>I4/mmm</i> for La<sub>1.81</sub>Sr<sub>0.19</sub>CuO<sub>4</sub> (x = 0) to orthorhombic with space group <i>Fmmm</i> for La<sub>1.81−x</sub>Sr<sub>0.19</sub>Eu<sub>x</sub>CuO<sub>4</sub> (x = 0.2, 0.3, 0.4), and to a substantial shrinking of the c-axis from 13.2446 Å (x = 0.0) to 13.1257 Å (x = 0.4). Such structural changes were accompanied by a dramatic decrease in the superconducting critical temperature, Tc, from 29.5 K for x = 0 to 13.8 K for 0.2. For x ≥ 0.3, no superconductivity was detected down to 4 K.
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