NONSTOICHIOMETRIC OXIDE FORMATION IN SYSTEM Nd-Ni-O.
Abstract
The non-stoichiometric compositions Nd2-xNiO4-3x/2+d were obtained using coprecipitation method from nitrates solutions by K2CO3 followed by calcination of the obtained blend at 900°С (10 hours). It was found that full coprecipitation of ions begins at mole ratio of coprecipitated ions to precipitator n=1,75 in range рH=10-10,2.
The thermogravimetric investigations established that coprecipitated carbonates decompose in the four stages.
The first – (25 – 392ºС), removing of сrystallisation and adsorbed water evaporation. The second - (392 – 520ºС), OH— - groupes decomposition. The third (622 - 720 ºС), carbonates groupes decomposition. At 850ºС - neodymium nickelate phases formation.
According to X-ray phase analysis Nd2NiO4.392(5) consists of orthorombic neodymium nickelate and a small of Nd2O3 impurity (specific reflex at d=0,3026 nm).
Nd2NiO4.392(5) unit cell parameters - a=0,545(0)nm, b=0,536(8) nm, с=0,123(3)nm, space group Bmab.
Samples Nd1.9NiO4.113(5) and Nd1.8NiO4.006(5) consist of non-stoichiometric phase Nd2-xNiO4+d with neodymium ions deficient in sublattice.
The orthorhombic unit cell parameters for Nd1.9NiO4.113(5) - a=0,541(9) nm, b=0,535(4) nm, с=0,123(2) nm, Nd1.8NiO4.006(5) - a=0,541(5) nm, b=0,535(4) nm, с=0,123(2) nm.
The stabilization of non-stoichiometric neodymium nickelate phases likely is due to ion vacancies formation.
Nd2-xNiO4-3x/2+d samples with 0,2<x£0,5 are polyphase and contain Nd2NiO4, NiO and Nd2O3. It was not observed Nd3Ni2O7 phase formation in our experimental conditions.
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