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Results indicate that zirconium and hafnium nitride halides crystallize into hexagonal shapes and with lithium intercalation they are transformed to solvent free superconductors. Data further show that the electronic structures of the crystals vary.

Pauling's second crystal rule is used to predict the distribution of anions in mixed oxyanion systems such as oxynitrides and oxyhalides with diverse compositions and structure types. The results are presented in a plot correlating the charge of the anions obtained from the observed occupancies in crystallographic positions with the calculated bond strength sums for these sites.

Research has been conducted on the superconducting compounds which contain transition metals other than copper. The synthesis and structural characterization of the (SrO)(SrNbO (sub)2-x N) (sub)n (n= 1,2) has been carried out and the results indicate that these compounds constitute Ruddlesden-Popper strontium niobium oxynitrides and provide layered parent structures.

Electronic flexibility and colossal magnetoresistance effects are discovered in the perovskite oxynitrides EuW[O.sub.1+x][N.sub.2-x] and ammonolysis of [Eu.sub.2][W.sub.2][O.sub.9] has produced scheelite-type intermediates EuW[O.sub.4-y][N.sub.y] with a small degree of nitride substitution. Both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio, EuW[O.sub.1+x][N.sub.2-x] phases order ferromagnetically at 12 K and colossal magnetoresistances (CMR) are seen in the least doped sample.

The perovskite oxynitrides EuM[O.sub.2]N (M = Nb, Ta) are prepared and their coupled colossal magneto-resistive and capacitive effects are studied. The results have shown an excellent potential for large magneto-responses in materials like EuNb[O.sub.2]N, which has combined the large [Eu.sup.2+] spin and the off-center instability of [Nb.sup.5+] enhanced by bonding to nitride.

Rietveld method was used to refine the crystal structure of the n = 1 member of the Ruddlesden-Popper family (SrO)(SrNbO2N)n. The refined stoichiometry obtained by neutron diffraction for the n = 1 compound is Sr2-NbO3.28N0.72, indicating that a mixed-valence state for niobium, intermediate between +4 and +5 that results from a nitrogen deficiency with respect to the nominal stoichiometry.

Unusual subextensive configurational entropies that vary with particle size and tend to zero per atom in macroscopic samples are predicted for AMO3-zNz oxynitrides with perovskite type crystal structures. These materials are crystallographically disordered on the atomic scale, but local anion order produces chains of M-N-M bonds that undergo a 90° turn at each M cation, giving rise to subextensive entropies in materials such as SrTaO2N, LaNbON2, and EuWO1.5N1.5. A general Pauling ice-rules formula is used to calculate the extensive molar entropies for other cases such as SrMoO2.5N0.5 and BaTaO2N. The subextensive oxynitrides are usefully classified as showing an "open order", related to the correlated order of displacements in ferroelectric perovskites such as BaTiO3. This raises the possibility that further open-ordered oxynitride or molecular structures may be accessible, and other states such as spins and charges may also show novel open orders. [ABSTRACT FROM AUTHOR]

A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO1+xN2-x. Ammonolysis of Eu2W2O9 yields scheelite-type intermediates EuWO4-yNy with a very small degree of nitride substitution (y = 0.04) and then EuWO1+xN2-x perovskites that show a wide range of compositions -0.16 ⩽ x ⩽ 0.46. The cubic lattice parameter varies linearly with x, but electron microscopy reveals a tetragonal superstructure. The previously unobserved x < 0 regime corresponds to oxidation of Eu (hole doping of the Eu:4f band), whereas x > 0 materials have chemical reduction of W (electron doping of the W:5d band). Hence, both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio. EuWO1+xN2-x phases order ferromagnetically at 12K, and colossal magnetoresistances (CMR) are observed in the least doped (x= -0.04) sample. Distinct mechanisms for the hole and electron magnetotransport regimes are identified. [ABSTRACT FROM AUTHOR]

Studies the synthesis and structures of two members of the family of Ruddlesden-Popper strontium niobium oxynitrides. X-ray and electron diffraction patterns of oxynitrides; Magnetic susceptibility for as-prepared and reduced sample of the oxynitrides; Averaged formal oxidation states for niobium; Crystal structure determination of the oxynitrides; Use of Rietveld analysis.

The article discusses the coupled colossal magneto-resistive and capacitive effects on a perovskite oxynitrides EuNbO2N. It highlights the synthesis done on the material to prove the earlier contentions raised. Furthermore, it reveals that there is an excellent potential magneto-responses in materials like EuNbO2N in combining the large EU 2+ spin and the off-center instability of Nb 5+ enhanced by bonding to nitride.

Europium tantalum perovskite oxynitrides were prepared by a new high-temperature solid-state synthesis under N 2 or N 2 /H 2 gas. The nitrogen stoichiometry was tuned from 0.63 to 1.78 atoms per Eu or Ta atom, starting with appropriate N/O ratios in the mixture of the reactants Eu 2 O 3 , EuN and Ta 3 N 5 , or Eu 2 O 3 and TaON, which was treated at 1200 °C for 3 h. Two phases were isolated with compositions EuTaO 2.37 N 0.63 and Eu 3 Ta 3 O 3.66 N 5.34 , showing different crystal structures and magnetic properties. Electron diffraction and Rietveld refinement of synchrotron radiation X-ray diffraction indicated that EuTaO 2.37 N 0.63 is a simple perovskite with cubic Pm 3̅ m structure and cell parameter a = 4.02043(1) Å, whereas the new compound Eu 3 Ta 3 O 3.66 N 5.34 is the first example of a triple perovskite oxynitride and shows space group P 4/ mmm with crystal parameters a = 3.99610(2), c = 11.96238(9) Å. The tripling of the c-axis in this phase is a consequence of the partial ordering of europium atoms with different charges in two A sites of the perovskite structure with relative ratio 2:1, where the formal oxidation states +3 and +2 are respectively dominant. Magnetic data provide evidence of ferromagnetic ordering developing at low temperatures in both oxynitrides, with saturation magnetization of about 6 μ B and 3 μ B per Eu ion for EuTaO 2.37 N 0.63 and the triple perovskite Eu 3 Ta 3 O 3.66 N 5.34 respectively, and corresponding Curie temperatures of about 7 and 3 K, which is in agreement with the lower proportion of Eu 2+ in the latter compound.

The development of new synthetic methodologies of perovskite oxynitrides is challenging but necessary for the search of new compounds and the investigation of new properties. Here, we report a new method of preparation of the perovskite LaTaON 2 that has been investigated as a pigment and photocatalyst for water splitting. The synthesis proceeds through the solid-state reactions under N 2 at 1500 °C between La 2 O 3 , LaN, and Ta 3 N 5 or between LaN and TaON, which are completed after 3 h and lead to sintered, highly crystalline samples with particle sizes up to 1 μm. Nitrogen-deficient samples LaTaO 1+ x N 2- x with x ≤ 0.35 are prepared by changing the N/O ratio in the mixture of reactants. Electron diffraction, synchrotron diffraction, and neutron diffraction studies on stoichiometric and nitrogen-deficient compounds indicate that they crystallize in the monoclinic space group I 2/ m with lattice parameters for LaTaON 2 of a = 5.71458(7), b = 8.05987(10), c = 5.74772(6) Å, and β = 89.982(3)°. The three anion sites of the I 2/ m structure are partially occupied by oxygen and nitrogen, with a preference of nitride for two positions with occupancies of 77 and 88%. This anion distribution is different from that reported in previous studies of samples prepared by ammonolysis at lower temperature, suggesting that the synthesis conditions affect the anion order of this perovskite. Optical measurements indicate a band gap of about 1.9 eV, which is close to that observed in samples prepared by other methods. The determined dielectric permittivity for LaTaON 2 ε r ≈ 200, reported for the first time for a highly nitrided pseudocubic perovskite, is similar to that observed in perovskites with one nitrogen per formula.

A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO(1+x)N(2-x). Ammonolysis of Eu(2)W(2)O(9) yields scheelite-type intermediates EuWO(4-y)N(y) with a very small degree of nitride substitution (y = 0.04) and then EuWO(1+x)N(2-x) perovskites that show a wide range of compositions -0.16 0 materials have chemical reduction of W (electron doping of the W:5d band). Hence, both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio. EuWO(1+x)N(2-x) phases order ferromagnetically at 12 K, and colossal magnetoresistances (CMR) are observed in the least doped (x = -0.04) sample. Distinct mechanisms for the hole and electron magnetotransport regimes are identified.

New oxynitrides of RZrO(2)N (R = Pr, Nd, and Sm) have been synthesized via a direct solid-state reaction of R(2)O(3) with Zr(2)ON(2) at 1200-1500 degrees C under 2-3 GPa pressure. Powder X-ray diffraction shows that all three phases adopt an orthorhombic Pnma perovskite superstructure [a = 5.8537(1) A, b = 8.1707(1) A, and c = 5.7093(1) A for NdZrO(2)N] and the structural distortion increases with decreasing R(3+) ionic radius. This method may enable new mixed-metal oxynitrides to be synthesized without the use of nitriding gas atmospheres.