Accurate measurement of lattice constants and thermal expansion coefficients of halide perovskite alloy CH3NH3Pb(Br1-xClx)3

We accurately determined the lattice constants a and the thermal expansion coefficients alpha L of the mixed-halide perovskite CH3NH3Pb(Br1-xClx)3 as functions of the Cl--composition x. We used single-crystalline samples and performed X-ray photoelectron spectroscopy for the determination of x, and single-crystal X-ray diffraction for the determination of a. We found that mixed-halide single crystals were significantly Cl--rich compared to the precursor solutions from which single crystals were grown. The obtained Cl--composition-dependent lattice constant a(x) well follows the Vegard's law: a(x)=a0(1-x)+a1x , where a0=5.9366 +/- 0.0028 & Aring; , a1=5.6866 +/- 0.0027 & Aring; . In addition, from the temperature dependence of a(x), we determined the thermal expansion coefficients alpha L(x) of the mixed-halide perovskite CH3NH3Pb(Br1-xClx)3 for the first time.