Pr(3+) doping at the A-site of La(0.67)Ba(0.33)MnO(3) nanocrystalline material: assessment of the relationship between structural and physical properties and Bean–Rodbell model simulation of disorder effects

Bulk nanocrystalline samples of (La(1−x)Pr(x))(0.67)Ba(0.33)MnO(3) (0.075 ≤ x ≤ 0.30) manganites with a fixed carrier concentration are prepared by the sol–gel based Pechini method. Rietveld refinement of the X-ray diffraction patterns, shows the formation of single-phase compositions with rhombohedral symmetry. Upon Pr(3+) doping at the A-site, the unit cell volume and the B–O–B bond angles are reduced. FTIR spectra present a prominent absorption peak of the in-phase stretching mode (B(2g) mode) rising from the vibration of the Mn–O bond. Raman spectra at room temperature reveal a gradual shift toward lower frequencies in (E(g)) phonon mode with increasing Pr(3+) concentration. The M(T) measurements shows a clear ferromagnetic (FM)–paramagnetic (PM) phase transition with increasing temperature. An increase in resistivity and activation energy and a decrease in the metal–semiconductor transition (T(M–SC)) and Curie temperatures (T(C)) was observed as a consequence of Pr(3+) doping. The results are discussed according to the change of A-site-disorder effect caused by the systematic variations of the A-site average ionic radius 〈r(A)〉 and A-site-cation mismatch σ(2), resulting in the narrowing of the bandwidth and the decrease of the mobility of e(g) electrons. The magneto-transport behavior in the whole measured temperature and a magnetic field can be described by a percolation model, which is in agreement with the limited experimental data of the samples for x = 0.075, 0.15 and 0.30. The experimental results confirm that A-site substitution with Pr(3+) destroys the Mn(3+)–O(2−)–Mn(4+) bridges and weakens the double exchange (DE) interaction between the Mn(3+) (t(3)(2g)e(1)(g), S = 2) and Mn(4+) (t(3)(2g)e(0)(g), S = 3/2) ions. On the other hand, the Bean and Rodbell model has been successfully used to simulate the magnetization data of the samples with x = 0.15 and x = 0.22. The random replacement of La(3+) by Pr(3+) is shown to induce more disorder in the system, which is reflected in the increase of the fitted disorder parameter and spin value fluctuation. At a temperature close to room temperature, the maximum magnetic entropy change (ΔS(Max)) and the relative cooling power (RCP) of La(0.52)Pr(0.15)Ba(0.33)MnO(2.98) are found to be, respectively, 1.34 J kg(−1) K(−1) and 71 J kg(−1) for a 1.5 T field change.