Charge ordered Pr0.75Na0.25Mn1-xCrxO3 (x = 0-0.04) ceramics has been investigated to study the effect of Cr doping on structure and electrical transport properties as well as surface morphology which synthesized using the solid-state reaction method. X-ray diffraction (XRD) analysis revealed the crystalline phase of all samples consists of essentially single phase and crystallized in an orthorhombic structure. The Cr doping were influence the lattice parameters and the unit cell volume suggestively due to the different of ionic radius between Mn 3+ ions and Cr 3+ ions. DC electrical resistance measurement showed that, the x = 0 sample exhibited an insulating behaviour down to the lower temperature. Interestingly, the metal-insulator (MI) transition temperature for x = 0.02 and x = 0.04 samples were found to be around TMI~120 K and TMI~122 K respectively indicating the enhancement of double-exchange (DE) mechanism as a result of weakening the Jahn-Teller (JT) effect which caused the charge ordered (CO) state to be weakened. scanning electron microscope (SEM) images of Pr0.75Na0.25Mn1-xCrxO3 compound showed the morphology of the samples were quite uniform suggestively due to the good crystalline nature.

Cr doping in charge-ordered Pr0.75Na0.25Mn1-xCrxO3 and Nd0.75Na0.25Mn1-yCryO3 have been synthesized using conventional solid-state method to investigate its effect on structural, electrical transport and magnetic properties. X-ray diffraction (XRD) analysis for both compounds showed that the samples were crystallized in an orthorhombic structure with Pnma group. The unit cell volume value      decrease as the Cr-doped increased indicating the possibility of Mn3+ ion was replaced by Cr3+ due to the different of ionic radius. The temperature dependence of electrical resistivity showed an insulating behavior down to the lower temperature the both parent compound (x = 0 and y = 0). Successive substitution of Cr at Mn-site in Pr0.75Na0.25Mn1-xCrxO3 manganites induced the metal-insulator (MI) transition temperature around TMI~120 K and TMI~122 K for x = 0.02 and x = 0.04 samples respectively suggestively due to the enhancement of double-exchange (DE) mechanism as a result of suppress the CO state. Analysis of resistivity data of dlnρ/dT-1 vs. T in Nd0.75Na0.25Mn1-yCryO3 manganite, showed a peak around 210 K and 160 K for y = 0 and 0.02 samples respectively while no peak was observed for y = 0.05 sample indicate the charge-ordered (CO) weakened. AC susceptibility, χ’ measurements in Pr0.75Na0.25Mn1-xCrxO3 exhibits paramagnetic to ferromagnetic-like with curie temperature, TC increases from 132 K for x = 0.02 to 141 K for x = 0.04 with Cr content indicate the suppression of CO state meanwhile in Nd0.75Na0.25Mn1-yCryO3 showed paramagnetic to anti-ferromagnetic transition as Neel temperature TN increases from 115 K for y = 0.02 to 125 K for y = 0.05.