Date of Award
Open Access Dissertation
Chemistry and Biochemistry
College of Arts and Sciences
Hans-Conrad zur Loye
Materials discovery via crystal growth is an active area of research that has led to the preparation of many novel materials along with the determination of their crystal structures. One sub-category in this diverse field of materials is the preparation of early transition metal reduced oxides. These reduced oxides often exhibit unusual electronic and magnetic properties. Due to the synthetic challenges associated with early transition metal reduction, new and facile methods to prepare reduced oxides is of great interest. These limitations can be overcome by using a carefully selected redox neutral flux, a vacuum sealed fused silica tube, and metal reducing agents, such as Zn, Mg, Ca, W and Mo. Our group has established two new synthetic routes for the efficient preparation of new reduced systems, including 1) a low temperature two-step hydrothermal method and 2) a high temperature molten flux method, and has been extremely successful in this endeavor.
A new reduced vanadium oxalate, Ba3[(VO)2(C2O4)5(H2O)6]•(H2O)3, 1, was synthesized via a two-step, mild hydrothermal method using oxalic acid as the reducing agent. This compound undergoes multiple single crystal to single crystal phase transitions as a function of water content to form Ba3[(VO)2(C2O4)5(H2O)4]•(H2O)2, 2, and Ba3[(VO)2(C2O4)5(H2O)2], 3, after heating 1 to 50 ºC and 100 ºC, respectively. In addition, exposing 1 to vacuum for 12 hours transforms it into 2, but not 3. Additionally, a new vanadium(III) phase, NaV(HPO4)2, was synthesized using acetic acid/copper acetate as reducing agents using a one-step hydrothermal method.
Single crystals of Ln4V5-xZnxSi4O22 (Ln = La, Ce, Pr, and Nd), Ln4Mo2O11 (Ln = La, Ce), were grown from molten chloride fluxes contained in evacuated sealed fused silica tubes. An in situ reduction of V(V) to V(III/IV) and Mo(VI) to Mo(V) as well as of Ce(IV) to Ce(III) was achieved employing Zn metal as the reducing agent. Ce4V4.77Zn0.23Si4O22, to the best of our knowledge, is the first example of a ceriumcontaining mixed-valent vanadium silicate. Additionally, neutron diffraction studies of the flux mediated crystal growth of La4Mo2O11 were carried out in order to better understand the in situ reduction via flux crystal growth, which showed the appearance and disappearance of intermediate products as well as the isolation of the final product, La4Mo2O11.
In situ synthesis of Eu(II) containing molybdates and tungstates, K0.094Eu0.906MoO4, K0.094Eu0.906WO4, EuMoO4, and EuWO4, were synthesized using Mo, W, and Zn as reducing agents. 151Eu Mössbauer spectroscopy was used to analyze the relative Eu2+ and Eu3+ content of the samples.
To improve the efficiency of the reduction, metals with high reducing power, such as Mg or Ca can be used too. Ba3Ti2Si4O14(Cl0.91O0.09), which contains Ti(III/IV), was synthesized using Mg as a reducing agent where as CaxLn1-xVSiO5 (Ln = Ce–Lu, Y) with V(III/IV) synthesized using Ca as a reducing agent. These materials have been characterized via powder and single crystal X-ray diffraction, magnetic susceptibility, and UV–vis spectroscopy.
Abeysinghe, D.(2017). Materials Discovery Of Reduced Early Transition Metal Compounds: Crystal Growth And Characterization. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/4373