Selenates ternary

Thousands of compounds of the actinide elements have been prepared, and the properties of some of the important binary compounds are summarized in Table 8 (13,17,18,22). The binary compounds with carbon, boron, nitrogen, siUcon, and sulfur are not included these are of interest, however, because of their stabiUty at high temperatures. A large number of ternary compounds, including numerous oxyhaUdes, and more compHcated compounds have been synthesized and characterized. These include many intermediate (nonstoichiometric) oxides, and besides the nitrates, sulfates, peroxides, and carbonates, compounds such as phosphates, arsenates, cyanides, cyanates, thiocyanates, selenocyanates, sulfites, selenates, selenites, teUurates, tellurites, selenides, and teUurides. 

Current methods for depositing ternary crystallite compounds include coevaporation of elements, or alloys, electrodeposition, reactive-sintering, and flash evaporation, which are often followed by sulphuriza-tion/selenization steps, at elevated temperatures. The current world record cell has been reported by NREL with an efficiency of 19.2% based on their patented three-stage process. ... 

Selenates, selenites, and tellurates. Uranyl selenates and selenites have been prepared and can be expected to have the same coordination features as the sulfates and sulfites. In addition to the selenate, U02Se04, the ternary selenite (U02)2(OH)2(Se03), has been reported to form in... 

A mechanism based on adsorption-reaction is in general agreement with the observed kinetics. New solid-state syntheses of crystalline selenates M2Se04 (M = K, Rb, and Cs) and antimonates, MSbOa (M = K or Rb), M3Sb04 (M = K, Rb, and Cs) involve treatment of the powdered superoxides, MO2, with Se02 and Sb203, respectively. These ternary oxides have been characterized by their X-ray diffraction patterns. 

The Barin tables are far more complete in coverage than any of the sources described above. All of the natural elements and their compounds are included. In addition to the substance types listed in USBM Bull 677, the Barin tables include a large number of ternary oxides - aluminates, arsenates, borates, chromates, molybdates, nitrates, oxy-halides, phosphates, titanates, tungstates, selenates, vanadates, zirconates, etc. - as well as cyanides, hydroxides, complex silicates and inter-metallic compounds. The only substances not included by Barin, for which tables can be found elsewhere, are the ionized-gas species and a limited number of gas species important only at very high temperatures, which are listed in the JANAF tables. For each table Dr. Barin gives references for each of the major thermochemical values employed (enthalpy of formation and entropy at 298 K, and heat capacity). Like the USBM Bulletins, no attempt is made to discuss the choice between conflicting data sources. 

Beginning in the late 1960 s, Giolito and Giesbrecht with coworkers imdertook a systematic study of the formation and properties of binary and ternary selenates of the rare earths. They have mainly used thermoanalytical and IR spectroscopic methods to characterize the solid compoimds. At about the same time singlecrystal X-ray diffraction data have become available from other laboratories. Extensive thermoanalytical studies have, also been carried out by Nabar and CO workers. 

The only ternary rare earth selenate which has been fully characterized by a single-crystal X-ray diffraction study appears to be the triammonium scandium selenate (NH4)3[Sc(Se04)3], which corresponds to the complex anion [Sc(Se04)3] (Valkonen and Niinisto, 1978 table 15). The crystal structure... 

Although the existence of the ternary selenates has been known since the last century, the first systematic studies on their properties have been carried out recently. These studies focused on their thermal stabilities are are summarized in table 16. In all cases the decomposition mechanism has been explained by the... 

Consequently, we will start with the description of oxo-selenates(VI) in the first part of this chapter, and then move on to the major part of the article which is dedicated to oxo-selenates(lV). The oxo-selenate(Vl) section provides the description of various binary compounds in the first part (section 2.1), and will discuss the respective ternary phases in the second part (section 2.2). Among the properties of oxo-selenates(VI) (section 2.3), the thermal behavioitr firms out to the best irrvestigated one. The oxo-selenate(IV) section also starts with the binary species (section 3.1). These are the best investigated oxo-selenates so far, so that more details can be given, for example on synthesis (section 3.1.1) of the R2(Se03)3 type compoimds (section 3.1.2) which are completely known. Subsequent sections are devoted to the anionic (section 3.2) and cationic (section 3.3) derivatives of oxo-selenates(IV) and finally, properties of oxo-selenates(lV) will be discussed. The last section summarizes orrr present knowledge of mixed-valent oxo-selenates(IVA ) which, unfortunately, remairts limited. 

Fig. 6. Chains ofthe composition J)[Pr(Se04)4/2(H20)5] (top) and ( [Ce(Se04)4/2(H20)5] layers (bottom) in the ternary oxo-selenate(VI) pentahydrates (NH4)Pr(Se04)2-5H20 and RbCe(Se04)2 5H20.

As anionic derivatives of selenates(IV), those compounds shall be considered in which some of the selenite (or diselenite) anions are replaced by halide ions (section 3.2.2) or even by complex anions (section 3.2.3). In a strict sense, the oxide-selenites mentioned in section 3.1 are anionic derivatives of selenates(lV) with SeOj groups replaced by oxide ions. However, they belong to the binary system R203/Se02 and that s why they were discussed in that context and not within this section. On the other hand, the oxide-halides will be discussed here because they are members of the ternary systems R203/RX3/Se02 (see section 3.2.2). 

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