Preparation Of Perovskite-type Oxide LaCoO₃ And LaFeO₃ Nanofibers Via Electrospinning

LaCoO3 and LaFeO3 nano-fiber has a wide range of applications to fields of high-temperature,superconducting material and GMR material, which caused wild public attention. And in terms of preparation of the nano-fibers, electrospinning is a simple, inexpensive and widely used method in the preparation of a nano-structure. And in appropriate conditions, the electrospinning technique can be controlled for a certain range fiber diameter, orientation and other characteristics, sintering in its objectives could be obtained about several tens of nanometers to a fiber such as high specific surface area, and unique and excellent electromagnetic performance, which combined with the electrospinning sol-gel technology for preparing nano fibers have broad application prospects. This article applies electrospinning combined with sol - gel technology, to explore the preparation of perovskite LaFeO3 and LaCoO3 and means of nanofibers and the best synthesis conditions. Following are the main results:1.With PVP/LaCoO3 (or LaFeO3) electrospinning precursor solution wasA concentration were 8wt%, 10 wt% and 15wt% PVP precursor solution made the case for electrostatic spinning. The results show that, 8wt% of the PVP/LaCoO3 (or LaFeO3) composite fiber diameter is very small (an average of about 150nm), but the fiber adhesion phenomenon obviously, and the process of spinning off the phenomenon of small droplets thrown clear; 10wt% of PVP/LaCoO3 (or LaFeO3) composite fiber diameter medium (average of about 300nm), fiber thickness is more uniform, there was no adhesion phenomenon; 15wt% of PVP/LaCoO3 (or LaFeO3) composite fiber diameter of the thickest (average 500nm or so), and the fiber thickness distribution is very uneven, because the needle always been difficult to plug the slow spinning speed spinning, and sometimes large droplets flung collection plate, the variation of fiber diameter with the PVP concentration is increased gradually thicken, in general, 10wt % of PVP/LaCoO3 (or LaFeO3) precursor solution spinning the best.2.To PVA/LaCoO3 electrospinning precursor solution wasA concentration of 8wt%, 10wt% and 12wt%PVA solution was made of the precursor electrospinning respectively. The results show that, 8wt% of PVA/LaCoO3 fiber diameter and smaller, but the fiber is easy to break, and thrown off the spinning phenomenon of small droplets obvious; by 10wt% of PVA/LaCoO3 middle diameter fiber, fiber thickness than uniform, dripping phenomenon reduced; 12wt% of PVA/LaCoO3 thickest fiber diameter, and fiber thickness distribution is very uneven, it is difficult to spin, the spinning speed is very slow, there are large droplets flung collection of board ; The relationship between changes in fiber diameter with PVA concentration gradually thicken, in general, 10wt% of PVA/LaCoO3 precursor solution spinning the best.3. Electrospinning of factorsAs the voltage rises in the spinning process, the hanging drop becomes smaller, the Taylor cone tip upward retreat, tending to disappear. At the same time along with the voltage rises, bead-like formations begin to change more, spinning taper, drip point of diminishing. Spinneret to the receiver board to receive power from the spinning of smaller beads to more Web results, and the diameter of electrospun fiber dispersion is also great as the distance increases, the average electrospun fiber diameter decreases.4. Sintered and test resultsThe concentration of 10wt% of PVP/LaCoO3, 10wt% and 10wt% of PVA/LaCoO3 the PVP/LaFeO3 composite nano-spinning into the tube furnace, in order to maintain the morphology of fibers obtained to prevent fiber breakage, useing 2℃/min of slow heating rate, in 400~1000℃for 1 h, respectively Sintering of stay.From XRD spectra, we can see that, when calcined at 400℃, the perovskite LaCoO3 characteristic peak appear, as well as the characteristics of hexagonal structure La2O3 peak. To 600℃La2O3 has disappeared, only some weak residual miscellaneous peak exsit, so the characteristic peak of LaCoO3 is not very clear. At 900℃to 1000℃, the cubic perovskite peaks of LaCoO3 are clearer, and stronger at 1000℃, indicate that the higher the temperature, phase the better.It is necessary to test results into the wire through SEM images on the premise of phase formation. SEM images of PVP/LaCoO3 before sintering were Precursor fibrous structure samples, the fiber diameter range between tens to several hundred nanometers, the diameter distribution is not too uniform, the smallest have reached several tens of nanometers, most fibers in a few hundred nanometers or so, because the PVP polymer complex, is smooth fiber surface. Fiber is very long, so it is difficult to find the breakpoint in the SEM images, which is consistent with the principles of electrospinning. Sintered at 400℃, the sample maintain fibrous structure,as PVP, acetic acid and other organic components easy to volatile, decompose and release in the form of gas (such as CO2,H2O, etc.) , fiber shrink, mainly in the 100nm diameter, at the same time the grain of LaCoO3 has started to form causes the fiber shape change greatly, the surface which can be seen from the graph becomes no longer as smooth as the surface of fiber before sintered. From the SEM images of PVP/LaCoO3 fiber calcined at 600℃for 1h show that fiber become thinner obviously to about 50nm, while fiber surface becomes rough up, this is due to the formation of LaCoO3 grain in large quantities, evolution of considerable heat, fiber morphology can occur more changes. After calcined at 800℃for 1h the fiber can be seen a little thicker than that under 600℃, between about 50~100nm, this is because the fiber in the complete decomposition of organic ingredients will not change already, and with temperature rises the size of the grain of LaCoO3 grows, becomes a great grain leads to a more rough surface of the fiber. After sintered at 1000℃the sample turn into a pearl chain structure, the surface become roughness further, fiber reaches complete crystallization, with a large diameter. Meanwhile as the high temperature, more than fiber capacity,the fiber can not maintain slender,as well as the phenomenon of fracture is serious.For PVA/LaCoO3 and PVP/LaFeO3 sintering nano-spinning there are similar test results.In summary, this paper by electrospinning technique and sol-gel method using different concentrations of polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA) as a complexing agent, the perovskite structure of LaFeO3 and LaCoO3 nanofiber for about 100nm was prepared after electrospinning and sintering. This simple and practical preparative technique in the preparation of oxide nano-fiber has a good future.