ПРОЦЕССЫ ДЕСОРБЦИИ КИСЛОРОДА В ВЫСОКОПЛОТНОМ ЛАНТАН СТРОНЦИЕВОМ МАНГАНИТЕ La0.6Sr0.4MnO3-d

Characteristic properties of the formation of physical - chemical properties of a manganite with the composition La0.6Sr0.4MnO3-d were considered. It was determined that two titration current minima depending on the heating rate and the partial pressure of oxygen (pO2) exist at different temperatures, heating rates and partial pressures of oxygen. It is supposed that extreme values of the titration current are caused by breaking of bands of anions existing in two different forms with the tetravalent manganese, as well as by the excessive superstoichiometric oxygen which partially compensate the presence of Mn4+ cations, and by oxygen recovering the electroneutrality of the system appearing due to a decrease of the charge value due to the introduction of Sr2+. It was established that the activation energy of oxygen diffusion is decreasing and reached the minimal value 241 kJ/mole at pO2=5 Pa, with a subsequent increase up to ~273 kJ/mole at pO2= 150 Pa and d=0,004, with the increase of oxygen defects concentration in the La0.6Sr0.4MnO3-d anion sublattice. Concentration dependence of the activation energy of oxygen diffusion is motivated by a formation of the stressed layer, placed near the surface of grains which are depleted with oxygen and at the same time they are a buffer for the oxygen diffusion.Расcмотрены особенности формирования физико-химических свойств манганита состава La0.6Sr0.4MnO3-d. В процессе выделения кислорода из La0.6Sr0.4MnO3-d при различных температурах, скоростях нагрева и парциальных давлениях кислорода существует два минимума тока титрования, зависящих от скорости нагрева и парциального давления кислорода. Экстремумы тока титрования, по-видимому, обусловлены разрывами связей между анионами, находящимися в двух различных формах, и четырехвалентным марганцем. Первая форма - это сверхстехиометрический кислород, частично компенсирующий присутствие катионов Mn4+. Вторая форма - кислород, восстанавливающий электронейтральность при введении Sr2+. При изменении концентрации кислородных дефектов в анионной подрешетке La0.6Sr0.4MnO3-d изменяется и энергия активации диффузии кислорода в интервале 0,0024≤d≤0,0031. Минимальное значение энергии активации при pO2=5 Па составляет 241 кДж/моль. При pO2=150 Па и d=0,004 она возрастает до ~ 273 кДж/моль. Концентрационная зависимость энергии активации диффузии кислорода обосновывается образованием напряженного слоя, расположенного вблизи поверхности зерен, обедненных кислородом и одновременно являющимся буфером для его диффузии

PROCESSES OF OXYGEN DESOPRPTION IN HIGH-DENSITY LANTHANUM-STRONTIUM MANGANITE La_0.6Sr_0.4MnO_3-_d

Characteristic properties of the formation of physical - chemical properties of a manganite with the composition La0.6Sr0.4MnO3-d were considered. It was determined that two titration current minima depending on the heating rate and the partial pressure of oxygen (pO2) exist at different temperatures, heating rates and partial pressures of oxygen. It is supposed that extreme values of the titration current are caused by breaking of bands of anions existing in two different forms with the tetravalent manganese, as well as by the excessive superstoichiometric oxygen which partially compensate the presence of Mn4+ cations, and by oxygen recovering the electroneutrality of the system appearing due to a decrease of the charge value due to the introduction of Sr2+. It was established that the activation energy of oxygen diffusion is decreasing and reached the minimal value 241 kJ/mole at pO2=5 Pa, with a subsequent increase up to ~273 kJ/mole at pO2= 150 Pa and d=0,004, with the increase of oxygen defects concentration in the La0.6Sr0.4MnO3-d anion sublattice. Concentration dependence of the activation energy of oxygen diffusion is motivated by a formation of the stressed layer, placed near the surface of grains which are depleted with oxygen and at the same time they are a buffer for the oxygen diffusion