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Hydrothermal Synthesis And Characterization Of The Chrome Complex Oxides

Posted on:2014-02-20Degree:MasterType:Thesis
Country:ChinaCandidate:S WangFull Text:PDF
GTID:2231330395498089Subject:Inorganic Chemistry
Abstract/Summary:PDF Full Text Request
Recently, orthochromite perovskites have been reported widely in the chemicaland physical aspects. This kind of materials has many potential applications accordingto its excellent physical properties.Compared with other synthesis methods, hydrothermal preparation is of great interest due to its numerous merits,for instance,lower temperature one-step synthesis proced-ure, easy handling, controllable particle size distribution etc.However, compared to magnates, the orthochromite perovskites are hard toprepare under the hydrothermal condition due to the highly distorted structure of thematerials. On the other side, the relatively weak stability of octahedral Cr in aqueoussolution may also play a part here. Meanwhile, the alkalinity beyond may promoteCr3+oxidizing to a certain extent, which make the chromate hard to prepare underhydrothermal method with KOH as mineralizer. As a result, by the limits of kineticsand thermodynamics the synthesis of the orthochromites requires significantly highertemperatures (and therefore greater autogeneous pressures).There have been fewer studies focused on the hydrothermal synthesis ofchromite perovskites and most of them used the unconventional hydrothermalmethods(like with the custom built hydrothermal autoclave system to reach300℃and more higher temperature). At present, it is a choke point to prepare the chromateperovskites under mild conventional hydrothermal method.In this paper, we study the synthesis of LaCrO3and its solid solutions doped withSr (La0.9Sr0.1CrO3and La0.8Sr0.2CrO3) and RCrO3(R=La, Pr, Nd, Sm, Dy, Ho) seriescompounds under relatively mild hydrothermal conditions (~260℃) in Teflon-linedstainless steel autoclave. And we characterize the samples as-made by XRD, EDS,SEM and ICP, the results of characterizations demonstrate the samples have uniformgrading and high purity. The temperature dependence of electrical conductivities ofthe samples La1-xSrxCrO3(0≤x≤0.2), measured using a DC four-probe method,shows that the conductivities increase with Sr doping, and the behavior of each sample can be ascribed to the small polaron hopping conduction mechanism. We alsoreport here the preliminary magnetic properties of all the samples as made.
Keywords/Search Tags:perovskite, chromate, hydrothermal synthesi
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