Hall mobility and defect structure in undoped and Cr or Ti-doped CoO at high temperature

Point defect diagrams for pure and doped cobalt oxide $$ {\hbox{C}}{{\hbox{o}}_{{{1} - }}}_{\delta }{\hbox{O}} $$ in the temperature range of 1,173–1,673 K (I)

“…Assuming that the ratio of mobilities is μ h /μ e =0.1 [4], in Fig. 4 [17] and for Cr c on t e nt y Cr ¼ 1 Á 10 À2 mol=mol p o i n t s -( e m p t y t r i a n g l e) , 3·10 −2 mol/mol-(empty square) -dotted line and y M 0 ¼ 0-solid line these pressures are higher than the oxide decomposition pressure, which is in accordance with the presence of a minimum of the electrical conductivity in Co 1Ày M y À Á 1Àd O oxide doped with Cr and Ti [21].…”

“…A good consistency obtained for the content y M ¼ 3 Á 10 À2 mol of M 3+ ions can be surprising (dotted line). As it transpires from the results of the studies of Nowotny et al [33,44,45], as well as from the studies of other authors [21,31], the maximal solubility of Cr in CoO is at about 1%. Thus, it can be expected that on the crystal surface, the formation of a thin layer of spinel CoCr 2 O 4 or nuclei of this phases occurs [44].…”

“…From the studies on electrical conductivity and on the Seebeck effect, it transpires that the ratio of mobility of electrons vs. electron holes is about μ h /μ e =0.1 [4,8,11,21,22,26]. The oxygen pressure p…”

“…The points mark the results of studies for pure Co 1Àd O: (solid diamond)-Schmalzried et al [5,6], (solid circle)-Fisher and Tannhauser [8], (empty diamond)-Fisher and Wagner [9], (empty square)-Eror and Wagner [10], (empty triangle)-Bransky and Wimmer [11], (solid triangle)-Sykora and Mason [15], and (solid square)-Constant et al [16] ences of δ and of the concentration V 00 Co  à vs. p O 2 are also marked, for the dope content of y M ¼ 3 Á 10 À2 mol=mol-dotted line. The quantity of dope was chosen in order to allow for the comparability with the results of the studies on the deviation from the stoichiometry in a doped oxide, Cr 2 O 3 , performed by Mrowec and Grzesik [17] and with the studies on the electrical conductivity performed by many authors [21,31,33,34]. The defect diagrams at other temperatures look similar.…”

“…In order to determine this structure, the studies on the deviation from the stoichiometry were performed, using the electrochemical method [5,6] and the thermogravimetric method [7][8][9][10][11][12][13][14][15][16][17], as well as the studies on electrical conductivity [3,4,[7][8][9][10][11][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] and on the Seebeck effect [4,9,11,16,22,30,33,34]. Similar characters of the relation of the deviation from the stoichiometry and the electrical conductivity on the oxygen pressure (the value of exponent near 1/4) were the basis for adopting the thesis that in the whole range of the oxide's existence the dominating defects are single-ionized cobalt vacancies and electron holes.…”