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La 0·7 Ca 0.3− x Sr x MnO 3 :Ag 0.2 (LCSMO:Ag) ceramics with varying strontium (Sr) content (x = 0.0165, 0.03, 0.05, 0.07, and 0.1) were synthesized using a combination of sol–gel and solid-state doping methods and studied as colossal magnetoresistance materials. Significant improvements in the peak temperature coefficient of resistivity (TCR) and resistivity (ρ) were observed across all ceramic samples when the mol% of Sr was adjusted. The low ρ and large TCR values resulted from a combination of two factors. First, the presence of Sr led to the increase in the grain size and decrease in the number of boundaries, which improved the electrical transport and reduced the boundary scattering effects. This resulted in additional improvement in the grain arrangement order. Second, the cell volume (V cell) and octahedron volume (V oct) both decreased first and then increased. The MnO 6 octahedron underwent gradual deformation into a flattened shape, which facilitated carrier migration and increased electrical sensitivity of the material. The ceramic with x = 0.03 maintained high and stable TCR values in different working environments, both without a magnetic field (TCR o , 54.76% K−1) and in the presence of a vertical field (TCR ⊥ , 33.33% K−1). Furthermore, the material exhibited a low resistivity and a higher insulator–metal transition temperature (T p). Performance differences among the samples were comprehensively and systematically explained by conducting cross magnetic field tests with field directions parallel and perpendicular to the flat surface of the bulk material, respectively. Overall, the findings of this study indicate that these ceramics act as promising candidates for future applications in information storage devices and magnetic sensors. [ABSTRACT FROM AUTHOR]

In this account, polycrystalline La 0.7 (Ca 0.27 Sr 0.03)MnO 3 :Ag 0.2 (LCSMO:Ag) ceramics were synthesized by the sol-gel method followed by solid-state doping. The Ag amounts doped into grain boundary and cell lattice could be adjusted by changing the sintering temperature from 1000 °C to 1500 °C. The temperature coefficient of resistivity (TCR) and magnetoresistance (MR) of the obtained LCSMO:Ag ceramics were tested under cross magnetic field with directions parallel and perpendicular to the flat of bulk. The difference between TCR and MR values reached their maxima at sintering temperature of 1450 °C, meaning that degree of lattice distortion reached maximum value. The combined data from X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrated that Ag was doped into the grain boundary and lattice cell, and Ag played an important role during the process. The influence of Ag-doping on TCR and MR suggested that degree of lattice distortion can be adjusted by doping, leading to change in isotropic ceramics into anisotropic ceramics without damage. Application of parallel magnetic fields shifted the application temperature to room temperature, and response sensitivity of the ceramics to magnetic field further increased. Overall, these findings look promising for future applications in photoelectric and magnetic devices. [ABSTRACT FROM AUTHOR]

A series of La 0.64 RE 0.06 Ca 0.3 MnO 3 (RE = Nd, Eu, Gd, Dy, and Er) polycrystalline ceramics were prepared by the sol-gel method. The effects of the substitution element types on the structure, electrical transport properties and magnetic properties of the polycrystalline ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and other tests. The results show that as the ionic radius of the substitute elements decreases, the cell volume decreases, the grain size increases, the peak resistivity increases exponentially, the metal insulator transition temperature decreases linearly, the temperature coefficient of resistance (TCR) shows a trend of first decreasing and then increasing, the peak TCR of these samples reaches 43.4%, and the magnetoresistance (MR) shows a trend of gradually increasing, reaching 92.4% at a 1 T magnetic field. Based on small polaron hopping（SPH） model, variable range hopping（VRH）model and the phase separation mechanism, fitting the resistivity temperature curves of polycrystalline ceramics shows that elemental doping changes the electrical transport properties mainly by influencing the crystal structure and thus the activation energy Eα. When the radius of the doped element ions is large, the peak TCR is close to dρ/dT max , so the main influence is the paramagnetic (PM) phase resistance. When the radius of the dopant element ions is small, the peak TCR is far from dρ/dT max , so the main influence is the ferromagnetic (FM) phase resistance. [ABSTRACT FROM AUTHOR]