Four silver(I)-germanates have been prepared from the binary components Ag2O and GeO2 by solid state reaction applying elevated oxygen pressures (2500-3000 bar). Ag6Ge2O7 isisostructural to Ag6Si2O7(II) [P21,a= 16.268(3), b = 10.021(2), c = 5.320(1) Å, β = 90.85(2)°], Ag10Ge4O13 to Ag10Si4O13 [PT, a = 11.731(3), b = 9.147(3), c = 8.727(4) Å, a = 99.33(2), β = 91.61(1), γ = 114.27(2)°].
According to the results of preparative investigations and chemical analysis there are two further phases in the system Ag2O/GeO2 of compositions ′Ag2GeO3′ and ′Ag2Ge2O5′.
The new oxide LiAg3O2 was prepared using oxygen pressures of about 300 at. The crystal structure, determined by single crystal X-ray investigations, consists of branched O—Ag—O—Ag chains; Li is coordinated by distorted, edge-sharing oxygen tetrahedra. The space group is Ibam; α = 5.974 Å, b = 9.945 Å, c = 5,694 Å.
K3NO3 and RbsNO3 were prepared by solid state reaction of equimolar mixtures of K2O/KNO2 and Rb20/RbN02, respectively. According to X-ray powder photographs their crystal structures are derived from the perovs-kite structure. K3NO3 is isostructural with Na3NO3 (a = 521.7 pm, Z = 1), Rb3NO3 represents a tetragonally distorted variant with a = 770.5, c = 550.8 pm and Z = 2.
High temperature Guinier photographs of As2O5 indicate a continuous phase transition to HT-As2O5, which is accomplished at 305 ± 3 °C. The crystal structure of HT-As2O5 has been derived from the low temperature form; space group and lattice constants are P41212-D44 and a = 857.2 pm, c = 463.6pm (310 °C), respectively. According to symmetry considerations, the phase transition is expected to be of pure ferroelastic-paraelastic type (422F 222).
Low temperature Guinier photographs of Na3NO3 ( + 20° → - 140 °C) indicate two phase transitions to M-Na3NO3 and T-Na3NO3 at - 53±3°C and - 122±3°C, respectively. During the phase transitions the main structural features (NO2-[ONa3]: antiperovskite type of structure) remain unchanged. The dynamically disordered NO2- in H-Na3NO3 order to form an antiferroelectric arrangement in T-Na3NO3. Crystal structures for M-Na3NO3 and T-Na3NO3 are proposed.