NONSTOICHIOMETRIC OXIDE FORMATION IN SYSTEM Nd-Ni-O.

Анотація

The non-stoichiometric compositions Nd_2-xNiO_4-3x/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 Nd₂NiO_4.392(5)  consists of orthorombic neodymium nickelate and a small of Nd₂O₃ impurity (specific reflex at d=0,3026 nm).

Nd₂NiO_4.392(5) unit cell parameters -  a=0,545(0)nm, b=0,536(8) nm, с=0,123(3)nm, space group Bmab.

Samples Nd_1.9NiO_4.113(5) and Nd_1.8NiO_4.006(5) consist of non-stoichiometric phase Nd_2-xNiO_4+d with neodymium ions deficient in sublattice.

The orthorhombic unit cell parameters for Nd_1.9NiO_4.113(5)  - a=0,541(9) nm, b=0,535(4) nm, с=0,123(2) nm, Nd_1.8NiO_4.006(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.

Nd_2-xNiO_4-3x/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.