The application of an electric field (300 V/cm) on PbMoO4 crystals at direct contacts generates a coloration spreading from the anode. The absorption at about 2.2 eV vanishes after annealing in air. The current‐voltage characteristic exhibits a linear relationship under special conditions. Annealing in reducing nitrogen atmosphere drastically enhances the conductivity and gives rise to the occurrence of a quadratic characteristic. Oxygen vacancies are assumed to be involved in trapping processes during the injection of carriers. A narrow peak in the photoconductivity spectrum at 380 nm is ascribed to the transition of an electron from the 6s2 state of the lead ion to the 2e molecular orbital of the oxocomplex ion with a subsequent thermal activation. Some other bands in the longwave region are correlated to (MoO4)3− centers and oxygen vacancies.
I n Ca (NbO,), crystals glow peaks of thermally stimulated conductivity (TSC) can be obtained even without previous X-irradiation. A crystal is cooled to low temperatures with a constant voltage Ud applied. At 100 K the voltage is changed to Ui and the TSC is measured while the sample is heated with a constant rate. When Ud $r Ui, the metal-insulator-metal system is in the nonsteady state, and two glow peaks are observed. The thermally stimulated currents can be either positive or negative, or negative at low temperatures and then positive a t higher temperatures. However, when u d = Ui, the system is in the steady state, and no glow peaks appear. A qualitatjive explanation of the measurements is given. It is based on a model that assumes blocking contacts and an inner relaxation in the insulator. I n Ca(NbO,),-Kristallen lassen sich Glowmaxima der thermisch stimulierten Leitfiihigkeit (TSL) auch ohne Rontgenbestrahlung erzielen. An einen Kristall wird beim Abkiihlen eine Spannung Ud angelegt und diese bei 100 K auf eine Spannung Ui umgeschaltet. Sodann wird die TSL beim Aufheizen mit konstanter Heizrate aufgezeichnet. F u r u d #= Ui ist das Metall-Isolator-Metall-System in keinem stationaren Zustand und man erhiilt zwei Glowmaxima. Die thermisch stimulierten Strome konnen sowohl positiv als auch negativ sein. Ferner konnen sie bei tiefer Temperatur negativ und bei hoherer Temperatur positiv sein. Dagegen ist fur Ud = Ui das System im stationaren Zustand und man erhiilt keine Glowmaxima. Eine qualitative Erklarung der MeBergebnisse kann aufgrund eines Modells gegeben werden, welches sperrende Kontakte und eine innere Relaxation im Isolator annimmt.
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