A single crystal EPR study of W5+ in triclinic Na0.33WO3, a recently discovered compound, has been carried out at about 15 K and 9.2 MHz. The EPR spectrum consists of two strong resonances and several weaker resonances whose relative intensities are sample-dependent. The total W5+ concentration is approximately 1000 at. ppm. The principal g-tensor components and the 183W hyperfine splitting constants for the two strong resonances are |g1|=1.695±0.003, |g2|=1.659±0.003, |g3|=1.636±0.003 [|A2|≃(61±8)×10−4 cm−1] and |g1|=1.676±0.002, |g2|=1.630±0.002, |g3|=1.593±0.002 [|A3|≃(52±4)×10−4 cm−1] for resonance 1 and resonance 2, respectively. The hyperfine splitting constants could only be determined in a few orientations because of either lack of resolution or interference of weaker resonances. It is proposed that the observed resonances are due to different W5+ point defects in the Na0.33WO3 host. This work represents the first evidence of W5+ in the tungsten bronzes.
A. X-band EPR Spectrometer 28 B. The Cavity Coaxial Cable Assembly (CCCA) 30 1. General description 2. The dewar top cap 3. The cavity a. General description b. The cylindrical TE^^^ mode c. The quality factor Q d. Calculated Q-values e. Experimental Q-values 4. The coaxial cable 5. The coupling loop 64 6. The modulation coils 67 C. Heat Transfer to the Cavity 74 D. Temperature Control and Temperature Measurements 77 E. Sample Holders and Sample Orienting Device Block diagram of EPR spectrometer 29 Cavity coaxial cable assembly and sample holder ' 31 Upper part of the cavity coaxial cable assembly 32 Lower part of the cavity coaxial cable assembly 33 Assembled OFHC-copper cavity 35 Disassembled OFHC-copper cavity 36 Schematic field distributions, a and b, and wall currents, c, in a cylindrical TE_,, mode cavity 38 Mode chart for a right circular cylinder of radius, a, length, d, and resonance frequency, f 40 Mode shape factor Q S/X vs. 2a/d several TE^np "^des 44 Equivalent circuit of a reflection cavity. The EPR cavity is represented by a RLCcircuit, the coupling is represented by a transformer with turns ratio n, and Rq represents the characteristic impedance of the waveguide plus the generator (E) impedance Configurations of the cylindrical quartz filled TEg^^ mode OFHC-copper cavity Block diagram of test circuit used for determination of resonance frequency, fq, and loaded quality factor, 46
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