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A study of the Au197 Mossbauer resonance is reported as a function of oxygen stoichiometry for gold‐doped YBa2Cu3O7−δ. Three separate Mossbauer features are identified and correspond respectively to gold metal particles, Au3+ in a square‐planar Cu(1) site, and Au+ in a two‐ligand c‐axis coordinated Cu(1) site. All the gold successfully incorporated into the 123‐structure is trivalent at full oxygenation (O7.02) but is reduced as a function of decreasing oxygen content until only monovalent gold remains at the orthorhombic to tetragonal transition (≊O6.4). A significant fraction of the Au3+ in the oxygenated sample resides near grain boundaries and is precipitated as gold particles upon reduction. The observation of monovalent gold in the reduced sample is the first report of the existence of Au+ with uniquely oxygen coordination for any material.

The Mossbauer effect of the 37.2 keV transition of 121Sb and the 23.88 keV γ transition of 119Sn has been employed to study the electronic configuration of Sb and Sn ions in the conducting materials BaSn1−xSbxO3 for 0≤x≤0.2. A single‐resonance absorption line is observed for each isotope. The isomer shifts change slightly with Sb content and fall in the region corresponding to Sb(V) and Sn(IV) valence states, respectively. The Sb isomer shift (IS) of 7.5 mm/s is significantly depressed (∼1 mm/s) relative to its value in a typical Sb(V)O6 chromophore and indicates a high degree of covalency, corresponding to significant 5sm5pn hybridization. The Sn IS of 0.1 mm/s indicates that the Sn atoms in BaSn1−xSbxO3 are more covalent than in BaSnO3. Charge disproportionation of the Sn and Sb into Sn(II) and Sn(IV) or Sb(III) and Sb(V) has not been observed.

The Mossbauer effect of the 37.2 keV γ transition of 121Sb has been employed to study the electronic configuration of Sb ions in perovskite superconducting materials. The isomer shift (IS) changes with Sb content and falls in the region of the Sb(V) valence state. The IS increases from 7.00 mm/s for BaPb0.75Sb0.25O3 to 7.25 mm/s for BaPb0.75Bi0.25O3 and to 7.70 mm/s for (Ba0.6K0.4)BiO3 compounds, indicating a high degree of covalency, corresponding to changes in the 5sm5pn hybridization.

The Mossbauer effect of the 37.2 keV γ transition of 121Sb has been employed to study the electronic configuration of Sb ions in BaBi1−xSbxO3 with x=0.2, 0.4, and 0.5. A single resonance absorption line is observed. The isomer shift changes slightly with Sb content and falls in the region corresponding to an Sb(V) valence state. The isomer shift of 7.6 mm/s is significantly depressed (∼1 mm/s) relative to its value in a typical Sb(V)O6 chromophore and indicates a high degree of covalency, corresponding to significant 5sm5pn hybridization.

The Mossbauer effect of the 37.2 keV γ transition of 121Sb has been employed to study the electronic configuration of Sb ions in BaPb1−xSbxO3 superconducting materials. The isomer shift is constant as a function of Sb content and falls in the region correspoding to the Sb(V) valence state. The isomer shift of 7 mm/s is the lowest value yet observed for an Sb(V)O6 chromophore and indicates a high degree of covalency, corresponding to significant 5sm 5pn hybridization. The mixed valence state of an equal amount of Sb(III) and Sb(V) has not been observed.

The reduction of V ions in FeV3O8 from V5+(3d0) and V4+(3d1) to V4+(3d1) and V3+(3d2) by lithiation with n‐BuLi has been inferred by 57Fe Mossbauer effect. The Fe is localized and in the Fe3+ state for all x.

Lorentz microscopy and magnetization and Mossbauer effect measurements have been performed on a Cr‐Co‐Fe alloy having a two‐phase microstructure. Domains spanning many particles have been seen in samples whose Hc’s vary between 200 and 420 Oe. Walls appear to be ragged and are held back by particles. Magnetization and Mossbauer effect measurements indicate that the two phases constituting the microstructure in each of the three situations examined are ferromagnetic at ambient temperature. Based on these results it is inferred that domain‐wall–particle interaction is responsible for Hc.

We have demonstrated the presence of circulating circumferential currents in toroids of Tl‐Ba‐Ca‐Cu‐O superconductors at 77.3 and 90.2 K. The nominal composition was Tl1.5Ba2Ca2Cu3Ox; however, both the x‐ray diffraction pattern and the Meissner effect indicate the presence of more than one phase. The circulating current was found to decrease by 27% in 3.8×103 s. The nature of the above time dependence is not consistent with the presence of a simple ohmic resistance but rather indicates that a process such as flux creep is the cause of this decay. An estimated upper limit of the resistivity is 1.3×10−14 Ω cm at 77.3 K.

Mossbauer effect measurements of 57Fe in a Cr‐Co‐Fe alloy indicate the existence of two ferromagnetic phases at room temperature. The hyperfine field of the two phases differ by ∼11%. This result implies that domain‐wall–particle interaction is responsible for the coercive force, which is a different mechanism than in some Alnico alloys.

A new superconducting phase with an onset of 123 K and zero resistance at 121 K has been detected in the Tl0.5Ba2Ca2Cu3Oy multiphase system. The composition is reproducible and stable.

Single crystals of FexTaS2 (x≈0.28) are metallic, ferromagnetic (Tc=73±5 °K), and have a large coercive force of 55 kOe at 4.2 °K. Mossbauer measurements show the iron to be high‐spin Fe2+, with a distribution of hyperfine fields at low temperatures. Electron microscopic observations, together with these results, suggest the presence of iron clusters.