Synthesis and characterization of alkali silver chalcogenides and alkali rare earth germanates by supercritical fluids

Supercritical fluids are shown to be an excellent reaction media for the synthesis of novel solid state phases at intermediate temperatures. The first part of this dissertation describes synthesis and characterization of alkali transition metal chalcogenides. Three new alkali metal silver chalcogenides: CsAg₅Se₃, RbAg₃Te₂, and K ₃Cu₁₁Te₁₆ have been synthesized in supercritical ethylenediamine. CsAg₅Se₃ has an open channeled structure composed of silver and selenium atoms, and contains a cesium cation in the middle. RbAg₃Te₂, has anionic silver telluride with rubidium cations residing between these sheets. The building block of the K₃Cu₁₁Te₁₆ is a Cug(Te₂) ₆ pentagonal dodecahedral cage. Pb₆Sb₆Se ₁₇ was synthesized using supercritical water. The compound has square pyramidal ribbons made of (Pb, Sb)Se5.; We have also explored the chemistry of various metal germanates in supercritical water, particularly alkali rare earth germanates. Germanates are of interest because they have interesting microporous as well as optoelectronic properties. The first type of compounds were NaREGeO₄ (RE = Rare earth), where RE = Ho, Er, Yb, Tb, Tm, Lu. The unit cell has a band pattern which is characteristic of the olivine structure. NaRE₉(GeO ₄)₆O₂ (RE = Nd, Pr) is the second type of crystal structure. NaRE₉(GeO₄)₆O₂ is an oxyapatite and is composed of two unique Nd atoms with one of the Nd atoms disordered with Na resulting very interesting crystal structure. The last part of this dissertation describes some alkali vanadium germanates and their unique magnetic properties. LiVGe₂O₆ and NaVGe ₂O₆ the common pyroxene structure composed of VO₆ linear chains. The presence of these VO₆ chains through the structure results in the interesting magnetic property known as spin-Peierls distortion. Another structurally very interesting compound, Li₂VGeO₅ was synthesized. Li₂VGeO₅ has layers made of VO ₅ and GeO₄ groups with lithium residing between the layers. Experimental methods and techniques used to prepare the title solid state compounds are described. Structural and physical characterization of all the compounds is reported in detail in this dissertation.