We present a study of their structure, morphology, electrical and magnetic properties on the (Ca 1–xSr x) RuO 3 system for x = 0.0, 0.07, 0.10, 0.15 and 1.0. The samples were prepared by the solidstate reaction method in air at ambient pressure and heat in the 700 ℃ - 800 ℃ range for 48 h. By X-ray powder diffraction (XRD), we determine a solid solution until x = 0.15. Scanning electron microscopy (SEM) indicates that the particle size is 77 - 266 nm. The resistance measurements, as a function of temperature measurements from 7 to 300 K the (Ca 1–xSr x) RuO 3 system for x = 0.0, 0.07, 0.10, 0.15 and 1.0 show a metallic behaviour. We can even observe that the resistance of the samples is due to the partial substitution of Sr 2+ ions and Ru ion valence. Finally, the sample x = 0.07 has a magnetization applied high field to 10 K, whereas that to 300 K does not have a magnetization.
The coexistence of superconductivity and magnetic order in the rutheno-cuprates compounds like RuSr2GdCu2O8 (Ru-1212) and their properties has been extensively studied [
The nano-crystalline samples of the CSRO system were synthesized by solid-state reaction technique at ambient pressure. The starting materials were: RuO2 anhydrous (99.9% STREM), SrCO3 (99.5% CERAC) and CaCO3 (99.99% BAKER). The structure of each reagent was corroborated by XRD. Prior to weighing, SrCO3 and CaCO3 were pre-heated during 10 - 20 min at 120˚C, in order to be dehydrated. The stoichiometric mixture of these compounds was done in an agate mortar in air, during 15 min, resulting inhomogenous slurry. The milled polycrystals were annealed between 700˚C and 800˚C in a thermolyne 46,100 furnace (±4˚C) during two days in air, to decompose the carbonates. The resultant nano-crystals of the samples with 0 ≤ x ≤ 1.0 were compressed into pellets (diameter 13 mm thickness 1.0 - 1.5 ± 0.05 mm), by the application of a pressure of 1/4 ton/cm2 for 15 min in vacuum. Specimens compacted were sintered at 800˚C during four days in air.
All reagents and samples were characterized by (XRD), using a Bruker-AXS D8-Advance diffractometer with λ (CuKα) = 1.54 Å radiation and graphite monocromator. Diffraction patterns were collected at room temperature on the 5˚ - 70˚ in a 2θ-range with a step size of 0.017 and time per step of 397 s. The change in morphology grain size in CSRO system obtained by different heat treatments, was observed by scanning electron microscopy (SEM) on a JOEL JSM-6610LV. The micrographs 50.00 KX, were taken with a voltage of 20 KV, current intensity of 1000 pA and WD = 10 mm. The Energy Dispersive X-Ray (EDX) was performed on the same equipment equipped with an Oxford/Link System electron probe microanalyser (EPMA). The standard four-probe method with DC resistance measurement was used as a function of temperature. The system is made up in a close-cycle refrigerator tool with conventional equipment for low-level electrical measurements. Continuous monitoring of all electrical parameters during a measurements cycle allows systematic errors in the resistance values to be detected in real-time, permitting clean R vs. T profiles to be obtained with no need of additional mathematical treatment to the experimental data [
The XRD patterns of (Ca1−xSrx) RuO3 system are shown in the
Finally, the net lattice parameters of (Ca1−xSrx) RuO3, x = 0.0, 0.07, 0.10, 0.15 and 1.0 system vary with the inclusion of the Sr-ion content and Ru ion coordination. Since the ionic radius of Ca2+ ion (Ca2+ = 1.34 Å) is lower than the ionic radius of Sr2+ ion (Sr2+ = 1.44 Å) [
The next step was the characterization of the samples achieved by SEM. The observed morphology is presented in
X | a (Å) | b (Å) | c (Å) | V (Å) |
---|---|---|---|---|
0.0 | 5.519(0) | 7.664(9) | 5.364(0) | 226.9(1) |
0.07 | 5.556(6) | 7.839(8) | 5.530(5) | 240.9(3) |
0.10 | 5.524(4) | 7.843(8) | 5.432(8) | 235.4(2) |
0.15 | 5.556(7) | 7.835(1) | 5.530(6) | 241.0(2) |
1.0 | 5.574(0) | 7.859(4) | 5.541(0) | 242.7(4) |
CaRuO3 compound does not exhibit ferromagnetism and its magnetic properties are still under discussion [
In the Ca1−xSrxRuO3 samples within the range of 0.07 ≤ x ≤ 0.15, the short-range ferromagnetic interactions appear. This indicates that the ferromagnetism has been suppressed through the process of substitution of Sr2+ ions by Ca2+ ions. For the compounds with large Ca2+ ions doping (x ≥ 0.7), no clear phase transition is discerned, and
only some irreversibility is observed in the magnetization curves of these materials. The disappearance of the long-range magnetic order is commonly related to the distortion of the RuO6 octahedra associated with the partial or total replacement of Sr2+ ions by Ca2+ ions, and the corresponding narrowing of the 4d bandwidth [
However, for Ca1−xSrxRuO3 (0.07 ≤ x ≤ 0.15) samples, the electrical resistance decreases with the incorporation of Sr2+ ions (2.1 × 10−3 Ω), giving less resistance than that of SrRuO3 (9.3 × 10−3 Ω). With the sample preparation described above, we did not find any superconducting phase. We observe the same behaviors that were reported for other similar compounds [
The magnetization at 10 K for x = 0.07 and 0.15 samples are based on the application of a magnetic field of 100 Oe, as shown in
phases CaRuO3 (1 − x) + (SrRuO3) (x), not one, which explains why both samples have the same transition FM to temperature at Tc―164 K.
Finally, as shown in
In this work, we obtained nano-crystalline samples of CSRO system by solid-state reaction in air at room temperature, in which a solubility up to x = 0.15 was observed. The SEM micrographs exhibit an almost-spherical grain size distribution from 77 to 266 nm. We also observed that the compounds of the CSRO system exhibit metallic behavior. However, for x = 0.07 and 0.15, the samples exhibit a FM transition to temperature Tc at ~164 K, indicating that the transition temperature decreases with increasing Sr ions concentration. Finally, we found that the x = 0.07 sample has a magnetization at temperature of 10 K, whereas at 300 K the sample does not present a hysteresis behavior.
This work was partially supported by CONACYT-80380, UNAM-IN109308.