Oxynitride rare-earths

Hampshire, S., Pomeroy, M.J. (2004), Effect of composition on viscosities of rare earth oxynitride glasses , J. Non-Cryst. Sol., 344, 1-7. 

We studied the effect of some modifying agents (NH4CI, alkali earths, rare earths, etc.) on the catalytic activity of oxynitride SHS ceramics. In some cases, the catalytic activity increases while the temperature of complete oxidation of hazardous contaminations... 

Antipcrovskites are known to form with rare earth elements, most notably the series ATTAIN (Af = C c. La. Nd, Pr, Sm [227], Those with the actual perovskite structure are oxynitrides LaWO(, N, 4 and NdWOu N, 4 [22.8] and have been the subject of some theoretical discussion [2291. The magnetic phase transitions can be explained by assuming that the Fermi level lies near a singularity in the electronic density of states [230], XANF.S and heat capacity measurements confirm these magnetic transitions [231, 232]. 

Challenged by the successful syntheses of dihalides of Sm and Yb as well as of Eu, synthetic inorganic chemists sought to make SmO and YbO. Brauer et al. [52] summarized earlier efforts but this experienced team of synthetic inorganic chemists was unable to synthesize lower oxides of Nd, Sm, or Yb. Soon thereafter a claim was made for synthesis of YbO, also with the NaCl structure [53]. Within months two of these authors admitted that YbO was actually Yb20C [54]. (Similarly, claimed PuO and AmO appear to be oxycarbides or oxynitrides.) McCarthy and White [55] provided a thermodynamic basis for the successfiil synthesis of EuO and EU3O4 but not of corresponding oxides of other rare earths. 

The rare earth-doped oxynitride glasses demonstrated higher densities and thermal expansion coefficients, but a substantially lower hardness, compared to the a- and P-Si3N4 single crystals. 

Checking over all of the rare earth-doped green to red phosphors with the requirements, we found that none of the rare-earth phosphors can fully meet them. For instance, very recent studies show that either Eu -doped nitride or oxynitride exhibits permanent failure in luminescence and phase structure [33, 34]. When exposed to high-pressure water steam, degradation starts at 150 °C, and the luminescence is quenched very quickly due to the phase decomposition [33]. For long-term applications, it is definitely meaningful to find candidates that can perfectly match all of the requirements. 

The formation of pure rare earth nitrides is often difficult to carried out, because the presence of oxygen can lead to the formation of oxynitrides. However under certain experimental conditions it is possible to form pure nitrides. 

REE (rare earth element) tantalum-titanium oxynitrides [20,25,26]... 

As for the corresponding iono-covalent ternary oxides, the structure of the quaternary R-M-O-N and higher oxynitrides will be advantageously described fi"om the coordination polyhedra of M atoms, the tetrahedra for example in silicates, the larger R atoms being located within the holes formed by the different arrangements of these structural units. Such a description is particularly well adapted to the case of tetrahedra and octahedra. Three types of environment for M atoms can be pointed out in the rare-earth-containing oxynitrides, namely tetrahedral, octahedral and cubic . 

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