The absolute necessity of an application of the high resolution for understanding of the physical nature of the strongly correlation systems having tendency to the phase separation is shown by the example of the electron-doped Sm_0.1Ca_0.9−xSr_xMnO₃ perovskite manganites study by powder neutron (NPD) and x-ray (XRPD) diffractions. The refinement of the room temperature XRPD data show a transition from Pnma for x≤0.4 to I4/mcm space group for 0.5≤x<0.8. The room temperature crystallographic parameters were obtained from analysis of the high resolution NPD data confirm with the preliminary x-ray study. The Pnma structures are slightly distorted (the distortion parameter [(a+c)/b√2] remains close to 1), whereas the cell parameters present a clear splitting in the I4/mcm space group (leading to a distortion [a√2/c] around 0.98). Nevertheless two kinds of Pnma lattices are observed, a>b/√2>c for x<0.2 and c>b/√2>a for x>0.2. A detailed (by 5 K temperature step) study of two compounds Sm_0.1Ca_0.9−xSr_xMnO₃ (x=0.3 and 0.6), belonging to each structural region, has been carried out on high intensity G4.1 diffractometer with the medium resolution. It demonstrates phase separations at low temperature, with mixtures of C- and G-type antiferromagnetisms (AF). The temperature dependence of the NPD patterns shows two magnetic transitions without structural ones for Sm_0.1Ca_0.3Sr_0.6MnO₃. At ~240K, peaks characteristic of C-type AF start to develop and at ~120K a peak characteristic of G-type AF appears. The data recorded with G4.1 for Sm_0.1Ca_0.3Sr_0.6MnO₃ were all refined by using one phase with the I4/mcm space group and C-type and then G-type antiferromagnetic structures were added for T~240 and 120K, respectively [leading to Mn magnetic moments of ≈2 and 1.1m_B, respectively (at 1.4K)]. The temperature dependence of the lattice parameters was studied from 1.4 to 300K showing a smooth evolution. The low temperature structure was then analyzed by using the higher resolution NPD-G4.2 diffractometer data. Two I4/mcm unit cells are needed to use to describe the low temperature state. Both unit cells are elongated along the c axis, the more distorted one corresponds to the main phase (70%) and C-type AF (with 2.3µ_B) and the more regular one (30%) is associated with G-type AF (2.4µ_B). The magnetic moments are along the c axis, corresponding to the longer Mn-O distances in the C-AF phase, and perpendicular to this axis in the G-type phase. The magnetic behavior of Sm_0.1Ca_0.6Sr_0.3MnO₃ is similar, with C- and G-type AFs establishing at ~150 and 70K, respectively. Nevertheless, accordingly to the G4.1 medium resolution data, for this compound a structural transition is associated with the magnetic one at 150K (from paramagnetic P-Pnma to C-AF-P2₁/m). At lower temperature, that is, around 70 K, the G-type AF starts to develop, without visible structural changes. The low temperature state (<70K) is thus described with one monoclinic cell associated with two AF components (with ≈2µ_B and 1µ_B for C and G, respectively). The high resolution G4.2-NPD data allow an improvement of the fit by adding a second crystalline phase of Pnma space group, corresponding to the G-type AF. At 1.5 K, the main part of the sample (~95%) corresponds to the P2₁/m space group and is associated with the C-type AF. The magnetic moments (2.1µ_B) are lying in the basal (x, z) plane in agreement with the distortion of the cell in this plane. The two MnO₆ octahedra of this monoclinic phase exhibit the same distortion: the smaller distance is the apical Mn-O (1.890 Å in both cases) and one of the equatorial ones is longer (1.920 or 1.921 Å) than the other one (1.896 or 1.895 Å). This elongation is associated with the d_3z2_−r2 orbital polarization, characteristic of C-type AF. Thus decreasing the temperature, the MnO₆ octahedra become more flattened and a strong distortion appears in the basal plane. So, it is shown, that only addition of the high intensity diffraction results by the data with the high resolution, lead to a coherent physical picture. The phase separation at low temperatures occurs as from the point of view of crystal, and magnetic structures. Each magnetic phase corresponds to the crystal phase and features of a crystal phase determine type of a corresponding magnetic phase. There are the strong relationships and the correlation between structures and properties in this phase separation Sm_0.1Ca_0.9−xSr_xMnO₃ series. 

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