NEUTRON HIGH RESOLUTION SINGLE CRYSTAL DIFFRACTION STUDY OF PHASE SEPARATION PHENOMENON IN La₂CuO_4+d

A.M.Balagurov¹⁾, V.G.Simkin¹⁾, V.Yu.Pomyakushin¹⁾, A.A.Zacharov²⁾ 1) Joint Institute for Nuclear Research, Dubna, Russia, 2) Russian Scientific Center "Kurchatov Institute" Moscow, Russia

Two La₂CuO_4+d single crystals with d=0.03 and 0.04 were studied in the temperature range of 10 K <= T <= 293 using the neutron high resolution Fourier diffractometer in Dubna. Diffraction patterns were measured for (00l) and(h00) /(0k0) directions in reciprocal space. At room temperature, the Bmab phase (h00) / (0k0) reflections were split due to twinning. In the crystal with d=0.04, the phase separation in the phases with Fmmm and Bmab symmetry was found, after cooling, as an additional splitting of the (0k0) peaks. In the crystal with d=0.03, the uniform state was preserved down to 10 K. The analysis of diffraction peak widths as a function of d-spacing offers the possibility of finding the dimensions of the coherent domains of coexisting phases in the d=0.04 crystal.

In the figure, the relative peak width vs. d_hkl is shown for the (00l) and (0k0) directions. The slope of the lines is connected with domain sizes which are close to 1000 Å in the (00l) and 1500 Å in the (0k0) directions, respectively.