A thermodynamic method is proposed to determine the optimal conditions for the synthesis of complex oxides employing self-propagating reactions. This permits estimation of heat effects and changes in Gibbs energy and entropy with the aid of standard thermodynamic functions, and also calculation of the temperatures of synthesized products in the adiabatic approximation.

The Bi2SrNb2O9, Bi4Ti3O12, and Bi4SrTi4O15 ferro- and piezoelectrics; BiNbO4 antiferroelectric; and compounds Bi5Nb3O15 and Bi12TiO20 were synthesized by combustion in oxidizer (metal nitrates) + oxide (Nb2O5, TiO2) + combustible (C6H10O5) mixtures. The combustion temperature of the reaction mixtures was between 1270 and 1620 K. Bismuth niobates were found to form more readily than bismuth titanates. The x-ray densities of the synthesized compounds are higher than those of the same compounds prepared by other methods.

The A(2)B(2)O(7)(A=Ca, Sr; B=Nb, Ta) refractory ferroelectrics were prepared by the redox reaction between A(NO3)(2) and polysaccharides under combustion conditions. The temperature in the combustion zone was found to exceed the melting points of the A(2)B(2)O(7) compounds. The formation of A(2)B(2)O(7) under combustion conditions is characterized by a short reaction time and high density of the final products. The process involves a few steps and yields phases with the highest melting points in the first step.

The types of compounds in the A2O3– B2O5 systems, where A = the p-, d-, and f-elements of Group III, the p-elements of Group V, and the d-elements of the fourth period in the tervalent state and B=Nb or Ta, are considered. An analysis of the methods of making the niobates and tantalates is given, their structure is described, and their physicochemical and electrophysical properties are reviewed. Special attention has been paid to the description of the rare-earth element meta-niobates, which exhibit the properties of electrets, and of the compounds of composition ABO4 (A = Sb, Bi; and B = Nb, Ta), which belong to a new group of ferroelectrics. Bibliography of 147 references.

AbstractDer Bildungsmechanismus von Praseodymmetaniobat beim Erhitzen der gemeinsam ausgefällten Hydroxide wird untersucht.

AbstractDie durch Umsetzung von Ti‐tetrachlorid mit entsprechenden Thiocyanaten in Acetonitril gebildeten, zum Teil als Acetonitril‐Solvate isolierten Produkte (I) werden IR‐ spektroskopisch als oktaedrische Hexaisothiocyanatotitanat(IV)‐Salze identifiziert.

AbstractDurch Analyse der IR‐Spektren wird gezeigt, daß die Nd‐Atome in Nd1/3NbO3 mit ABO3‐Struktur statistisch in den zu 2/3 aufgefüllten Schichten des Untergitters verteilt sind.

AbstractDie Titanatmolybdate (I) wurden durch Glühen von Mischfällungen der Hydroxide bei 900°C erhalten.

AbstractLa(NbO3)3 kristallisiert nach IR‐Daten tetragonal mit perowskitähnlicher Struktur.

AbstractDie gemeinsame Fällung von Nb‐ und Nd‐Hydroxid aus alkoholischen Lösungen wird untersucht.

The preparation and properties of rare earth titaniobates were investigated. It was found that rare earth titanoniobates with the composition LnTiNbC/sub 6/ (Ln is La, Ce, Pr, or Nd) can be obtained by roasting coprecipitnted metal hydroxides; the synthesis temperature is 850 to 900 deg C. The reaction between rare earth, titanium, and niobium hydroxides takes place at relatively low temperatures and begins during precipitation of the hydroxides. Rare earth titanoniobates of the cerium subgroup crystallize in the eschynite type. (auth)

AbstractDie Titelverbindungen (I) wurden durch Glühen von Hydroxidmischfällungen bei 850‐900°C erhalten.