Alkoxide Based Sol-Gel Processing of CMR Manganites
- PDF / 1,559,032 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 25 Downloads / 209 Views
FF10.6.1
Alkoxide Based Sol-Gel Processing of CMR Manganites Annika Pohl and Gunnar Westin Department of Materials Chemistry, Ångström Laboratory, Uppsala University, 751 21 Uppsala, Sweden.
ABSTRACT We have prepared a soluble manganese alkoxide, and used in the first all-alkoxide synthesis of Ca, Sr, and Ba substituted lanthanum manganites. The phase development from gel to target oxide was monitored by TGA, DSC, powder-XRD, FT–IR spectroscopy, and TEM-EDS. Here we present the effect of dopant on the phase development. It was found that the dopants influence the temperature of complete oxide formation (≥650°C). The main difference in phase evolution was seen in the 300-600°C range, where the formation of crystalline phases in trace quantities seemed to temporarily reduce the elemental homogeneity.
INTRODUCTION Chemical solution based processing, including sol-gel synthesis, is of great interest due to its relative cost effectiveness and simple to upscaling to industry scale. It benefits from a high control over stoichiometry and morphology, and it is in many aspects more flexible and less depending on the substrates than e.g. techniques based on vacuum technology or high temperature synthesis. In sol-gel processing the advantage of alkoxide precursors compared to e.g. acetyl-acetonates, acetates, or citric acid complexes, is that alkoxides normally yield more homogeneous and pure gels, thereby allowing for well-controlled phase development and low temperature conversion of the gel to oxide. In the year 2000 we reported the first soluble reactive manganese alkoxide, [Mn19O12(moe)14(moeH)10]·moeH.[1] The successful preparation of this compound has opened up new possibilities for sol-gel processing of manganese containing ceramics. We have used it in all-alkoxide synthesis of Ca, Sr, and Ba substituted lanthanum manganites as powders and thin films,[2,3] and shown that electronic transport properties and epitaxial quality of the films are comparable with films made by PLD.[4] To gain detailed knowledge about the sol-gel processes, the phase development from gel to target oxide was monitored by TGA, DSC, powder-XRD, FT– IR spectroscopy, and TEM-EDS. Here we present the effect of different dopants on the phase development.
EXPERIMENTAL DETAILS All synthesis and handling of precursors were made in a glove box, with an atmosphere of dry, oxygen-free argon. The anhydrous MnCl2, K, Ca La, Nd, Sr and Ba metal were used as purchased. The p.a. quality methoxy-ethanol (moeH), toluene, iso-propanol and ethanol were distilled over CaH2 under inert atmosphere. The lanthanum, neodymium, calcium, strontium and barium precursors were prepared by direct reaction of the metal with moeH. For La and Nd approximately 0.5 mg of HgCl2 was used as catalyst. The resulting alkoxide solutions contained
FF10.6.2
suspended fine particles, which were removed by centrifugation. The manganese precursor was prepared by dissolving K in moeH, followed by addition of MnCl2. After 24 hours of stirring, the mixture was centrifuged to separate the s
Data Loading...
