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In this paper, we discuss the structural and morphology properties of the solid-state prepared Pr0.67Ba0.33MnO3 perovskite manganite X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analyses were utilised to examine the structure, morphology, and chemical composition. The compound exhibits a single phase with an orthorhombic perovskite structure with a Pnma space group without any impurities. The refined cell parameters are a = 5.504 Å, b = 7.778 Å, and c = 5.528 Å (α = β = γ = 90° and a ≠ b ≠ c), therefore the cell volume is 236.723 Å^3. The tolerance factor is used to predict the stability of the Pr0.67Ba0.33MnO3, which is τ = 0.9241. Fourier transform infrared spectroscopy (FTIR) reveals that the Mn-O bonds appear at 600 cm^(-1). In addition, morphology SEM revealed that the grain sizes are heterogeneous, and the grain shapes are irregular. Using EDX technique, the percentage elemental composition of Pr, Ba, Mn, and O was determined. The values of the atomic percentages for each element are almost identical to the ratios of the elements during sample preparation.

The effects of Ga substitution at Mn site on electroresistance behaviour of La0.85Ag0.15MnO3 compound prepared by solid-state reaction method were investigated. X-ray diffraction (XRD) measurement were recorded at room temperature and refined by employing Rietveld techniques. Ferromagnetic to paramagnetic transitions behaviour have been observed from ac susceptibility results. Resistivity-temperature curve with different applied currents of 1 mA and 5 mA showed metal-insulator, MI transition temperature, TMI decreased with increased of the applied currents. The increased in applied current caused the maximum resistivity around TMI to be decreased for both samples indicated increased in charge carrier density which resulting in drop of resistivity, hence, enhanced double exchange mechanism. The electroresistance (ER) effects have been investigated. The result showed that the ER effect increases when Ga is substituted.

The microwave absorption properties of La0.85Ag0.15MnO3 prepared by solid state method was investigated. Analysis of X-ray diffraction data using a refinement technique confirmed the rhombohedral structure of the samples. The microstructure of the sample characterised from field emission scanning electron microscope micrographs showed irregular grain shapes with grain sizes ranging from 800 to 1500 nm. M-H curves revealed the weak ferromagnetic properties of the sample at room temperature. The real and imaginary parts of permittivity and permeability as well as microwave reflection loss were measured by a vector network analyser in the 8–18 GHz frequency range. The La0.85Ag0.15MnO3 sample showed a minimum reflection loss of –57.2 dB at 16.41 GHz, with a –10dB bandwidth (corresponding to reflection loss below –10 dB, or 90% absorption) of 2.67 GHz. The microwave absorption of La­­­­0.85Ag0.15MnO3 mainly arises from the conduction loss and domain wall motion which contributed to dielectric loss and magnetic loss, respectively.

Bi1.6Pb0.4Sr2Ca2-xEuxCu3Oδ cuprates superconductor doped with Eu nanoparticles (x = 0.0000, 0.0025, 0.0200 and 0.0500) were synthesized through conventional solid state reaction method. Crystalline sucrose was added during pelletization and burn at 400°C for two hours to create low density sample. The effect of doping Eu2O3 nanoparticles on the structural and superconducting properties by means of critical temperature (Tc), critical current density (Jc), X-ray diffraction (XRD) together with Field Emission Scanning Electron Microscopy (FESEM) and Alternating Current Susceptibility (ACS) were studied. Based on XRD analyses, the crystallographic structure has shown slightly changed from tetragonal to orthorhombic. The amount of 2223 phase gradually decreased with the increment of Eu concentration which indicates that Eu nanoparticles substitution favours the growth of 2212 phases. The resistivity measurements show that the highest Tcvalue for doped samples found at 90 K for x = 0.0025. The FESEM images showed that the plate-like grains become smaller and distributed randomly without specific alignment due to the increment of Eu concentration.

The electroresistance, ER effect of La0.85Ag0.15Mn1-xMoxO3 (x = 0.00 and 0.05) samples prepared using solid method are investigated. The increased of applied current from 5 mA to 10 mA does not change the metal-insulator transition temperature, TMI for both samples however decreased the resistivity in the temperature region of 50 K – 300 K. Both samples exhibit large ER effect at low temperature region. At TMI, the ER value is 75.5% (x =0) and decrease to 34.15% (x = 0.05). However, at 300 K, the value of ER increases to 57 % for Mo substituted sample, and the value decreases to 6.4% for the x =0 sample. The enhanced ER effect at 300 K may be due to the growth of conductive filaments under increased applied current. The increase of applied current may perturb the arrangement of magnetic inhomogeneity induced by Mo substitution, result in reduction of resistivity and lead to the observation of ER effect. These findings suggest potential application of La0.85Ag0.15Mn1-xMoxO3 (x = 0.05) in spintronic devices.

La0.7Ba0.3Mn1-xFexO3 (x = 0 and 0.02) were prepared by using solid state synthesis method to investigate the effect of Fe3+ substitution at Mn-site on electrical behaviour and structural properties. An analysis of X-ray diffraction, XRD data using refinement method shown both x = 0 and x = 0.02 samples were in single phased and crystallized in rhombohedral structural with Pnma space group. From ρ vs T curves shown resistivity decreased under increased of applied current of 10 mA to 20 mA for both samples in the temperature range of 20 K-300 K. The larger electroresistance, ER effect observed for x = 0.02 in temperature range of 20 K – 180 K compared to x = 0 sample is suggested due to the development of filamentary conduction path under increased of applied current. It is suggested that Fe substitution enhanced magnetic inhomogeneity which contribute to the growth of formation of conductive path under increased of applied current, lead to increase of ER effect. In the temperature range of 180 K – 300 K, the observed decreased in ER for Fe substituted sample (x = 0.02) is suggested due to the increased of scattering effect and reduction of available hopping site in metallic region and insulating region, respectively. Restriction in the movement of charge carrier had weakened the ER effect for Fe substituted sample. The observed ER effect indicates the compound has a potential for application such as for non-volatile memory elements.

Polycrystalline samples of Sr2Ni1−xMgxWO6 (x = 0.00, 0.02, 0.04, and 0.06) were prepared through a solid-state reaction method and the crystal structure, optical and dielectric properties of the samples were studied using X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS) respectively. Rietveld analysis of XRD patterns confirmed that the compounds crystallized in a tetragonal structure with a space group I4/m. The analysis revealed that the unit cell volume of the samples increased from 245.092 A3 to 245.273 A3 due to the larger ionic radius of Mg2+ (0.72 A) compared to that of Ni2+ (0.69 A). UV-vis analysis revealed that the band gap energy of the samples decreased from 3.30 eV to 3.24 eV as the doping amount increased from x = 0.00 to x = 0.06. This occurrence was attributed to the large size of Mg2+ that reduced the excitation distance for the valence electrons. FTIR analysis was performed for all samples and the characteristic absorption bands W–O6 confirmed the double perovskite structure. A dielectric characterization study using electrochemical impedance spectroscopy (EIS) revealed that the dielectric constant (e′) and dielectric loss (e′′) were higher in the low frequency area below 0.01 Hz and decreased upon increasing the frequency above 0.01 Hz until they reached a constant value at 1 MHz. At low frequency, the compound with Mg = 0.06 exhibited the highest value which was approximately 280. In addition, this compound showed the least dielectric loss at 0.01 Hz.

A study of the effects of Cerium oxide nanoparticle doped with BSCCO-2223 on the microstructure and superconducting properties was carried out. All samples were synthesized using solid state reaction method. Ce concentration is varied from x = 0.0 up to 0.1 in a general stoichiometry of Bi1.6Pb0.4Sr2Ca1-xCexCu3Oy. The samples were characterized structurally and electrically by X-Ray Diffraction (XRD) and four-point probe method respectively. XRD analysis shows that both (Bi,Pb)-2212 and (Bi,Pb)-2223 phases coexist in the samples having tetragonal crystal structure but changed to orthorhombic when x=0.10. The values of critical transition temperature, TC and critical current density, JC of the samples decreased with the increase in Ce concentration. The possible reasons for the observed degradation in superconducting and structural properties of Bi-2223 due to Ce nanoparticles addition were discussed.

The effect of yttrium (Y) substitution at La-site on structural, microstructural and electrical transport properties of (La0.7-xYx)Ca0.3MnO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) were investigated. Samples were prepared by conventional solid state reaction method and structural properties of the samples were obtained using the Rietveld refinement of X-ray diffraction data. X-ray diffraction patterns show orthorhombic distorted perovskite structures. Resistivity measurement results of the LaYCaMnO3 compounds show that metal–insulator transition temperature, TMI shifts to lower temperature while the resistivity increases by increasing Y3+ substitution. In the metallic region (T TMI), resistivity data were fitted to model of small polaron hopping conduction mechanism and the activation energy, Ea increased as Y substitutions increases. Keywords: Colossal magnetoresistance, Double exchange mechanism, Metal-insulator temperature, Activation energy, Conduction mechanism

The crystal structure and optical properties of Sr2NiWO6 double perovskite were studied. The polycrystalline Sr2NiWO6 sample was prepared through a solid-state reaction method. The structural and optical properties of the sample were determined using X-ray diffraction (XRD) and UV-Vis diffuse reflectance respectively. The Rietveld analysis of XRD confirmed that the compound existed in single phase and crystallized in a tetragonal structure with a space group I4/m. The analysis also revealed that the lattice parameter a and c were 5.562974 and 7.919822 A respectively. From the UV-Vis diffuse reflectance spectroscopy, the band gap energy of the sample was 3.29 eV.

This study reports the structural, morphological, and magnetic properties of ruthenium doping at the manganese site in Pr0.67Ba0.33MnO3 manganites. Rietveld refinement X-ray powder diffraction (XRD) data show that Pr0.67Ba0.33MnO3 and Pr0.67Ba0.33Mn0.9Ru0.1O3 crystallize in an orthorhombic perovskite structure with the Pnma space group. Doping with Ru yields an increment in the lattice parameter and unit cell volume. In addition, small changes in the Mn&ndash, O&ndash, Mn bond angle and bond distance are observed. Field emission scanning electron microscopy (FESEM) is used to examine the surface morphology of the samples. Fourier transform infrared spectroscopy (FTIR) reveals that the Mn&ndash, O and metal&ndash, oxygen bonds appear at the 600 and 900 cm&minus, 1 bands, respectively. The AC magnetic susceptibility measurement studies confirm that a paramagnetic (PM) to ferromagnetic (FM) transition exists at 130 and 153 K for the Pr0.67Ba0.33MnO3 and Pr0.67Ba0.33Mn0.9Ru0.1O3 samples, respectively.

The effect of Cr3+ substitution at Mn-site on the structure, magnetic and electrical properties of Bi0.3Pr0.3Ca0.4Mn1-xCrxO3 manganites were studied by using X-ray diffraction method, AC susceptibility and electrical transport measurements. All the samples with starting composition of Bi0.3Pr0.3Ca0.4Mn1-xCrxO3 (x = 0, 0.04, 0.08, 0.1, 0.12 and 0.14) were prepared using solid state method. R versus T curve shows that x = 0 sample exhibits a strong insulating behavior while Cr3+substitution at x = 0.08 induced metal-insulator (MI) transition at MI transition temperature (TMI) of 56 K. The substitution for x = 0.08 successfully weakened the hybridization effect which may related to strong ferromagnetic (FM) interaction between Cr3+ O Mn3+ as well as Mn3+ O Mn4+. Further substitution of Cr3+ for x = 0.1 increased the TMI to 58 K but decreased to 36 K for x = 0.12. Rietveld Refinement of the X-ray diffraction data showed a decreased of unit cell volume which indicated partial substitution of Cr3+ (0.615 A) at Mn+3(0.64 A) site. Susceptibility, χ′ versus temperature, T measurements, showed an increase of ferromagnetic-paramagnetic, FM-PM transition temperature, TC from 66 K (x = 0.04) to 125 K (x = 0.14) which suggested that Cr3+ substitution enhanced the growth of FM phase. Fitting of the experimental data in the metallic region to scattering models suggested scattering involving a combination of electron-electron, electron-magnon, Kondo-like spin-dependent scattering, and electron-phonon interaction are responsible for the observed resistivity behavior. On the other hand, fitting in the insulating region suggests that resistivity behavior obeys the variable range hopping (VRH) model below the charge ordered temperature, TCO for (x = 0) and TMI T θ D / 2 for x = 0.04–0.14 while at high temperatures involved small polaron hopping, SPH mechanism. Therefore, the enhanced double exchange mechanism (DE) indicates the substitution of Cr3+ increased the delocalization of charge carrier and destabilization of the CO-AFM state. It is suggested that such an increased of DE mechanism was related to the reduction of blocking mechanism which generated by the hybridization effect due to Bi 6s2 lone pair.

Nd0.75Na0.25Mn1−xNixO3 (x = 0 − 0.07) were synthesized using a conventional solid-state synthesis method to investigate the effect of Ni substitution on their magnetic and electrical transport properties. XRD analysis using the Rietvield refinement method showed an increase in unit cell volume with increasing Ni content, indicating the possibility of substituting Ni for the Mn site. For x = 0, magnetization measurements showed paramagnetic (PM) to antiferromagnetic (AFM) transition at the transition temperature, TN ∼ 185 K, which may be related to the presence of charge-ordering (CO) state. For Ni-substituted samples, ferromagnetic (FM) to PM transition was induced with Curie temperature (TC), increasing from 91 K (x = 0.01) to 115 K (x = 0.03), followed by decreases in TC to 60 K (x = 0.07). Electrical resistivity measurements showed that samples for x ≤ 0.01 exhibited insulator behavior while both x = 0.03 and 0.05 samples exhibited metal-insulator transition suggesting that the CO state is weakened. For x = 0.07, the sample shows re-entrant of insulating characteristic. Inducement of FM metallic (FMM) state, as well as increased of TC for x = 0.03 is suggested to be related to FM SE between Ni2+ and Mn4+, which suppressed the CO state, hence inducing double-exchange (DE)-like mechanism. In addition, an increase in resistivity was observed as temperature decreased below the resistivity minimum (Rmin) at Tmin ∼ 40 K for x = 0.05 is possibly due to the Kondo-like effect mechanism. On one hand, the M(H) curve showed the presence of a hysteresis loop for x = 0 and 0.01 at T= 60 and 80 K, indicating the presence of an unstable phase, which may be related with the CO-AFM phase. For x = 0.03, no hysteresis loop was observed, indicating the suppression of the CO-AFM. Intriguingly, for x = 0.05 and 0.07, small hysteresis loop was observed, indicating the possible presence of a minor AFM component. Further, the observed MR behavior in present studies can be understood as a result of a decreased scattering mechanism in the presence of magnetic field.

This paper presented the result of the structural analysis of Europium, Eu nanoparticles addition in low-density Bi(Pb)-2223 superconductor. Polycrystalline bulks with nominal composition Bi1.6Pb0.4Sr2Ca2Cu3Oy + xEu2O3 samples where x = 0.0, 0.2, 0.4, 0.6 and 0.8 wt% were prepared via solid-state reaction method. Low-density samples were created by adding crystalline sucrose into mixed powders and burn at 400 °C for two hours. The samples were characterized using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) for structural characterization while resistivity measurement was determined by using four-point probe method. Phase analysis by XRD indicated that both Bi-2212 and Bi-2223 phases coexist within the samples having a tetragonal crystal structure. As Eu concentration increases, the amount of Bi-2223 phase slightly decreased which signifies that Eu nanoparticles favour the growth of Bi-2212 phase. It was observed that the highest Tc and Jc values for the addition sample found at x = 0.2 wt%.

Polycrystalline Pr 0.75 Na 0.25- x K x MnO 3 ( x = 0, 0.05, 0.10, 0.15 and 0.20) ceramics were prepared using conventional solid-state method and their structural, magnetic and electrical transport properties were investigated. Magnetization versus temperature measurements showed un-substituted sample exhibited paramagnetic behavior with charge-ordered temperature, T CO around 218 K followed by antiferromagnetic behavior at transition temperature, T N ∼ 170 K. K + -substitution initially weakened CO state for x = 0.05–0.10 then successfully suppressed the CO state for x = 0.15–0.20 and inducing ferromagnetic-paramagnetic transition with Curie temperature, T C increased with x . In addition, deviation of the temperature dependence of inverse magnetic susceptibility curves from the Curie-Weiss law suggests the existence of Griffiths phase-like increased with x . Magnetization versus magnetic field curves show existence of hysteresis loops at T x = 0) and T x = 0.05–0.10), which related to metamagnetic transition occurring at critical field. Electrical resistivity measurements showed an insulating behavior for x = 0 sample while for x = 0.05–0.20 samples showed metal-insulator transition and transition temperature, T MI increased with x . The increased in T C and T MI are attributed to the increase in tolerance factor which indicates reduction in MnO 6 octahedral distortion consequently enhanced double exchange interaction.

The effects of Ba 2+ doping on the electrical and magnetic properties of charge-ordered Pr0.6Ca0.4MnO3 were investigated through electrical resistivity and AC susceptibility measurements. X-ray diffraction data analysis showed an increase in unit cell volume with increasing Ba 2+ content indicating the possibility of substituting Ba 2+ for the Ca-site. Electrical resistivity measurements showed insulating behavior and a resistivity anomaly at around 220 K. This anomaly is attributed to the existence of charge ordering transition temperature, $T^{\mathrm {R}}_{\text {CO}}$ for the x = 0 sample. The Ba-substituted samples exhibited metallic to insulator transition (MI) behavior, with transition temperature, T MI, increasing from ∼98 K (x = 0.1) to ∼122 K (x = 0.3). AC susceptibility measurements showed ferromagnetic to paramagnetic (FM-PM) transition for Ba-substituted samples with FM-PM transition temperature, T c, increasing from ∼121 K (x = 0.1) to ∼170 K (x = 0.3), while for x = 0, an antiferromagnetic to paramagnetic transition behavior with transition temperature, T N, ∼170 K was observed. In addition, inverse susceptibility versus T plot showed a deviation from the Curie–Weiss behavior above T c, indicating the existence of the Griffiths phase with deviation temperature, T G, increasing from 160 K (x = 0.1) to 206 K (x = 0.3). Magnetoresistance, MR, behavior indicates intrinsic MR mechanism for x = 0.1 which changed to extrinsic MR for x > 0.2 as a result of Ba substitution. The weakening of charge ordering and inducement of ferromagnetic metallic (FMM) state as well as increase in both T c and T MI are suggested to be related to the increase of tolerance factor, τ, and increase of e g −electron bandwidth as average ionic radius at A-site, increased with Ba substitution. The substitution may have reduced MnO6 octahedral distortion and changed the Mn–O–Mn angle which, in turn, promotes itinerancy of charge carrier and enhanced double exchange mechanism. On the other hand, increase in A-site disorder, which is indicated by the increase in σ 2 is suggested to be responsible for the widening of the difference between T c and T MI.

The effect of Bi substitution at La site on magnetic and transport properties of electron-doped La0.9−xBixTe0.1MnO3 was investigated. The samples were prepared through the standard solid-state method. Analysis of X-ray diffraction data using Rietveld refinement confirmed single-phase samples crystallized in rhombohedral structure. The undoped sample (x = 0) exhibited paramagnetic (PM) to ferromagnetic (FM) transition behaviour with Curie temperature, TC = 242 K and metal–insulator (MI) transition behaviour at MI transition temperature, Tp1 = 240 K. Partial substitution of Bi3+ at the La site for x = 0.05–0.15 decreased transition temperatures, TC and Tp1 to 150 and 115 K, respectively. By contrast, for x = 0.2, the sample showed fully insulating behaviour and PM–FM transition at TC = 140 K. A secondary resistivity peak observed for x = 0 sample at temperature, Tp2 = 194 K below Tp1 in ρ versus T curve was strongly suppressed by low Bi substitution of x = 0.05. In addition, enhanced magnetoresistance effect reaching 50% observed for the x = 0.2 sample was suggested due to spin-dependent interfacial tunnelling which enhanced under low magnetic field of 0.8 T. The observed rapid decrease in TC and Tp1 may be due to the role of 6s2 lone pair Bi3+ which produced a type of blocking effect due to strong hybridization between Bi (6s2) and O (2p) orbitals. This caused a reduction on the rate of eg electron-hopping process and elongation of Mn-O bond length, thereby weakening the double exchange mechanism.

Magnetic and electronic transport properties of Bi0.3-xLaxPr0.3Ca0.4Mn0.1Cr0.9O3 (0≤x≤0.2) manganites have been investigated by measurements of AC-susceptibility, resistivity and magnetoresistance. The samples were prepared using conventional solid-state synthesis method. Magnetic susceptibility versus temperature measurements showed all samples exhibit ferromagnetic to paramagnetic transition with Curie temperature, Tc enhanced from 111 K (x=0) to 174 K (x=0.2). Electrical resistivity measurements of the samples in zero field showed increase of metal-insulator (MI) transition temperature from 58 K(x=0) to 88 K(x=0.2). The increase in both Tc and TMI indicates enhancement of double exchange (DE) interaction involving Mn3+ and Mn4+ ions as a result of weakening of the hybridization effect between Bi3+ 6s2 lone pair with O orbital due to La3+ substitution. La substitution in the Bi-based compound is suggested reduce MnO6 octahedral distortion hence increasing delocalization of charge carriers. The observed variation in MR behavior due to La substitution indicates the substitution influence the MR mechanism of extrinsic and intrinsic behavior in Bi0.3-xLaxPr0.3Ca0.4Mn0.1Cr0.9O3 .

BiFeO 3 (BFO) doped La 0.8 Ag 0.2 MnO 3 ceramics were prepared by the conventional solid-state synthesis method to investigate the effect of BFO on transport and magnetic properties as well as its influence on magnetoresistance (MR). X-ray diffraction analysis showed a decrease in unit cell volume indicating partial substitution of some BFO into the La 0.8 Ag 0.2 MnO 3 (LaAgMO) lattice while results of scanning electron microscope (SEM) showed improvement in grains connectivity and formation of more regular shaped grains with BFO doping. Energy Dispersive X-ray emission (EDX) analysis showed BFO mainly segregates at the grains boundaries of LaAgMO. Resistivity and susceptibility measurements showed both metal–insulator transition temperatures, T MI and paramagnetic-to-ferromagnetic transition temperature, T c decreased with increased BFO content indicating weakening of the double exchange, DE mechanism. The temperature dependence of MR showed a small peak around T MI for all samples which is ascribed to the intrinsic MR effect. Below the MR peak, the MR increased almost linearly with decreasing temperature for all samples and this is ascribed to the phenomena of extrinsic MR. The highest MR% (at 40 K) was observed for the x =1.5% sample which showed a MR of more than twice that of the undoped ( x =0%) sample. This extrinsic effect is suggested to be related to improved spin polarized tunneling of conduction electrons between grains under external field as a result of improved spin alignment. It is suggested that BFO induced some kind of magnetoelectric coupling between BFO and LaAgMO leading to the enhancement process.

The electrical transport and magnetic properties of La0·8−xDyxAg0·2MnO3 (x = 0–0·1) colossal magnetoresistance ceramics have been investigated. All the samples showed transition from metallic behaviour at low temperatures to insulating behaviour at higher temperatures accompanied by ferromagnetic to paramagnetic transition. The Curie temperature Tc decreased from ∼288 K (x = 0) to ∼273 K (x = 0·1) with increasing Dy3+. For x = 0, double metal–insulator transition peaks were observed at Tp1 = 290 K and Tp2 = 261 K. Both peaks and Tc shifted to lower temperatures with increasing Dy3+, indicating that substitution of Dy3+ weakened the double exchange process and enhanced the Jahn–Teller effect. The magnetoresistance peak was observed around Tp1 for all the samples. The electrical behaviour at the metallic region below Tp2 was explained based on electron scattering models, while the Mott variable range hopping model was used to explain the resistivity behaviour above Tp1. The observed double peak behaviour in...

La 0.85− x Sm x Ag 0.15 MnO 3 ( x =0−0.2) ceramics were prepared using the conventional solid-state synthesis method to investigate the effect of Sm 3+ substitution on magnetic and electrical transport properties. Magnetic susceptibility versus temperature measurements showed all samples exhibit ferromagnetic to paramagnetic transition with Curie temperature, T c decreasing from 283 K ( x =0) to 164 K ( x =0.2) with increasing Sm 3+ . The observed slope in susceptibility, χ ′ versus temperature curves below T c indicates the possible presence of FM and AFM phases in the metallic region. In addition, a deviation from the Curie–Weiss law above T c in 1/ χ ′ versus T curves indicates the existence of a Griffith's phase in the x =0.05−0.2 samples due to the Sm 3+ ion substitution. The Griffith temperature, T G was found to decrease from 295 K ( x =0.05) to 229 K ( x =0.2). Electrical resistivity measurements of the samples in zero field showed transition from metallic behavior to insulating behavior as the temperature was increased. For x =0, two metal–insulator, MI transition peaks were observed at T p 1 =282 K and at T p 2 =250 K. Both peaks shifted to lower temperatures with the increase in Sm 3+ . The relative resistivity of the first peak to the second peak decreases with increasing Sm 3+ for x >0.05 while at x =0.2 the T p 1 peak was strongly suppressed. Magnetoresistance, MR was observed to weaken with Sm 3+ substitution. The metallic region of the ρ ( T ) curve of the x =0−0.15 samples was fitted to the model of electron–electron and electron–magnon scattering while the insulating region was fitted to the variable range hopping, VRH model. The resistivity behavior indicated that the substitution of Sm 3+ weakened the double exchange process and enhanced the Jahn–Teller effect. Our results indicated that the T p 1 peak is strongly related to the double-exchange mechanism while the T p 2 peak is suggested to originate from magnetic inhomogeneity.

Monovalent doped Pr 0.75 Na 0.25- y Ag y MnO 3 ( y = 0–0.10) manganite have been investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM) as well as DC electrical resistivity and AC susceptibility measurement to clarify the influence of Ag- doped on charge ordering (CO) state. XRD analysis revealed all samples consists of essentially single phase and crystallized in an orthorhombic structure with space group Pnma . SEM images of Pr 0.75 Na 0.25- y Ag y MnO 3 compound shows the successful substitution of Ag + ions with the enhancement of the grains boundaries and sizes as well as the compaction of particles. On the other hand, resistivity and susceptibility measurements showed that the y = 0 sample exhibits insulating behavior and anti-ferromagnetic. Interestingly, the ferromagnetic-metallic transition was observed for y = 0.05 due to the revival of double-exchange (DE) mechanism as a result of weakening the Jahn-Teller effect which caused the CO state to be weakened. However, increasing of Ag-doped up to y = 0.10 induce back its transition into anti-ferromagnetic insulating behavior suggestively due to the weakening of DE mechanism.

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.

Effects of Ti substitutions on superconductivity of Tl0.8Pb0.2Sr2−xTixCa0.9Y0.1Cu2O7 (x=0–0.7) and TlSr2−xTixCaCu2O7 (x=0–0.4) ceramics have been investigated. Tl0.8Pb0.2Sr2−xTixCa0.9Y0.1Cu2O7 (x=0) was observed to superconduct with T c onset of 90 K and T c zero of 21 K. Substitution of Ti with x=0.1–0.5 observed an increase in T c zero to 56–62 K with T c onset around 90 K. TlSr2−xTixCaCu2O7 (x=0–0.2) was not superconducting above 20 K but for x=0.3 superconductivity was observed with T c onset of 66 K and T c zero of 34 K.