Pr3+ doping at the A-site of La0.67Ba0.33MnO3 nanocrystalline material: assessment of the relationship between structural and physical properties and Bean–Rodbell model simulation of disorder effects. Issue 44 (15th August 2019)

• Record Type: Journal Article
• Authors: Oumezzine, Ma.; Sales, Herbet Bezerra; Selmi, Ahmed; Hlil, E. K.
• Is Part Of: RSC advances. Volume 9:Issue 44(2019)
• Page Start: 25627
• Page End: 25637
• Publication Date: 2019-08-15
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c9ra03494c
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : Bulk nanocrystalline samples of (La1− x Pr x )0.67 Ba0.33 MnO3 (0.075 ≤ x ≤ 0.30) manganites with a fixed carrier concentration are prepared by the sol–gel based Pechini method. Abstract : Bulk nanocrystalline samples of (La1− x Pr x )0.67 Ba0.33 MnO3 (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 (B2g mode) rising from the vibration of the Mn–O bond. Raman spectra at room temperature reveal a gradual shift toward lower frequencies in (Eg ) 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 eg 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+ (t32ge1g, S = 2) and Mn 4+ (t32ge0g, 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 (Δ S Max ) and the relative cooling power (RCP) of La0.52 Pr0.15 Ba0.33 MnO2.98 are found to be, respectively, 1.34 J kg −1 K −1 and 71 J kg −1 for a 1.5 T field change.