AAg2(M'xM1-x)[VO4]2: Synthesis and Structure-Property Relationships
Bratsch, Michaela 1988-
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This dissertation focuses on the synthesis and characterization of the AAg2(M’1 xMx)[VO4]2 series of compounds. These compounds are modifications of the parent type of compound, AAg2M[VO4]2. We have investigated the following parameters: i) the charge and size of the spacer ion (A), ii) the charge, size, and spin of the magnetic cation (M), and iii) the ratio (M’:M) of the solid solution series. In this research we specifically targeted the honeycomb (1:2) and kagome (1:3) lattices for the solid solution series, AAg2(M’1-xMx)[VO4]2. This provides an opportunity to tune the magnetic lattices by varying the M-site cations. The M-site cations utilized in this research are non-magnetic cations, Mg2+, Zn2+, In3+, and the magnetic cations, Ni2+ (S = 1), Co2+ (S = 3/2), Mn2+ (S = 5/2), Fe3+ (S = 5/2), and Cr3+ (S = 3/2). These cations provided an opportunity to probe different magnetic interactions in the compounds. The A-site cations that have been studied in this research were: Rb+, K+, Ba2+, Sr2+, and Ag+. With decreasing ionic radius, from Rb+ to Ba2+ the crystal structure is P3, and for Sr2+ and Ag+ the crystal structure is C 2/c. The structure and phase purity of the compounds were confirmed by XRD measurements. SEM-EDX was used to investigate the chemical compositions, and confirm the ratio of the M’ and M cations (stoichiometry). Raman spectroscopy in combination with DFT calculations has been conducted as a local probe to monitor the environment of the [VO4]3- unit and confirms that the surrounding of the [VO4]3- is in either a 1:2 (honeycomb) or 1:3 (kagome) ratio of M’:M. The thermodynamic properties of this series were investigated. These confirmed that the cations Ni2+ and Co2+ are ferromagnetic and follow a mean field theory behavior and that Mn2+, Fe3+, and Cr3+ are antiferromagnetic. The physical properties measurements indicate the bulk magnetic properties of the compounds are in agreement with the chemical composition. Neutron diffraction measurements performed on RbAg2(In1/3Cr2/3)[VO4]2 and AgAg2Cr[VO4]2 provided further information about the magnetic behaviors of these compounds.