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The structural, magnetic, and electrical transport properties of Sn-doped manganite La0.67Ca0.33Mn1−xSnxO 3−δ (x = 0, 0.01, 0.03, and δ ≈ 0.06) compounds were studied using X-ray powder diffraction, scanning electron microscopy, AC susceptometer and vibrating sample magnetometer measurements as well as four-probe resistance measurements. The specific heat was measured by the heat-pulse method. The Curie temperature TC and the metal-insulator transition temperature T M−I decreased nonlinearly with increasing Sn content. The TC and TM−I values, for the x = 0, 0.01, and 0.03 compounds were separated by 18.2 K, 66.3 K, and 10 K, respectively. The resistivity above T C for all of these compounds followed the Mott variable-range-hopping model. This allowed the estimation of the localization lengths of 2.2Å (x = 0), 1.33Å (x = 0.01) and 1.26Å (x = 0.03). The x = 0 and x = 0.01 compounds exhibited anomalies of R(T ) at corresponding T C and allowed the separation of the magnitude of the purely magnetic contribution to the resistance which for x = 0 was ≈ 5.7 Ω and for x = 0.01, ≈ 22.4 Ω. The specific heat of the Sn-free sample exhibited a sharp peak at TC. With increasing Sn content the peak at TC broadened and the area under the peak decreased. For x = 0.03 the peak was hardly detectable.

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