Tungsten-doped vanadium dioxide (VO 2 ) nanopowders were synthesized by thermolysis of (NH 4 ) 5 [(VO) 6 -(CO 3 ) 4 (OH) 9 ]‚10H 2 O at low temperature with, to the best of our knowledge, active white powdery tungstic acid (WPTA) used as a substitutional dopant for the first time. The change in electrical resistance due to the semiconductor-metal transition was measured from -5 to 150 °C by the four-probe method. Differential scanning calorimetry and the resistance-temperature curve of the nanopowders indicated that the phase transition temperature of VO 2 powders was 67.15 °C, but for W-doped VO 2 , the temperature was reduced to 26.46 °C. The results indicated that WPTA was found to be exceptionally effective as a dopant for reducing the transition temperature.
Abstract-The omnidirectional reflection characteristics of onedimensional (1D) superconducting-dielectric binary graded photonic crystals (PhCs) are studied by using transfer matrix method. The influences of thickness changing rate, numbers of periods, incident angles are analyzed. And the omnidirectional photonic band gaps are extended markedly in the 1D thickness-graded superconductingdielectric PhC.
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