On the Defect Structure of ZrO[sub 2] and HfO[sub 2]

Abstract

The defect structure of ZrO2 and HfO2 has been studied through measurements of electrical conductivity as a function of oxygen pressure. The electrical conductivity exhibits an unusual and complex oxygen pressure dependence, and to explain the results it has been proposed that these oxides are ionic conductors and that a coupled transport of oxygen vacancies and interstitials is faster than an independent transport of these defects. Thermogravimetric measurements on ZrO2 suggest that the nonstoichiometry of this oxide is more than a factor of ten smaller than that observed by Aronson.

Corrosion of Zirconium Alloys Used for Nuclear Fuel Cladding

“…Instead, the oxidizing species have to diffuse through the oxide layer. Observation of the zirconium oxide system at normal operating temperatures has confirmed that zirconium oxide is an n-type semiconductor (39,40) and that the oxide growth occurs by oxygen anion migration through the oxide film, with the formation of new oxide taking place at the metal/oxide interface (41, 42).…”

The importance of singly charged oxygen vacancies for electrical conduction in monoclinic HfO2

“…Experimental studies, for example, all report that the conductivity behavior as a function of oxygen partial pressure (pO 2 ) differs from that expected for an acceptor-doped oxide (aliovalent impurities in nominally undoped HfO 2 generally being of lower valence than Hf 4þ ). The explanations for the observed behavior also differ, requiring a coupled transport of oxygen vacancies and interstitials, 1 hafnium vacancies, 2,5 holes, 4 or Schottky disorder 3 to play a dominant role. None of these studies take into account the possibility of point defects in other than fully ionized charge states.…”

“…The electrical conductivity of nominally undoped, monoclinic HfO 2 (m-HfO 2 ) has attracted attention for decades, first out of fundamental interest, [1][2][3][4] but recently because of the application of HfO 2 as a gate dielectric or as the active element in resistive random access memories (ReRAMs). [5][6][7][8][9][10][11][12][13][14] Despite substantial attention, various aspects of the behavior are still under debate.…”

Crystal Growth and Photoluminescence Properties of Reactive CVD-Derived Monoclinic Hafnium Dioxide

“…The analysis of the optical emission data of this work and a comparison of them with the literature data obtained by other investigators allows us to find a correlation between optical emission and the defects in HfO 2 crystals. ,,,− The experimental data of this work and published previously are listed in Table . It was stated that the defects that can exist in monoclinic hafnium dioxide are vacancies and interstitial atoms and ions. , However, the calculated energy of hafnium vacancy formation is higher than that for oxygen vacancy formation. Based on DFT calculations, Foster et al stated that the presence of hafnium vacancies does not introduce any additional level in the gap.…”