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LnCrO3−xNx perovskites with Ln = La, Pr and Nd and nitrogen contents up to x = 0.59 have been synthesised through ammonolysis of LnCrO4 precursors. These new materials represent one of the few examples of chromium oxynitrides. Hole-doping through O2−/N3− anion substitution suppresses the magnetic transition far less drastically than Ln3+/M2+ (M = Ca, Sr) cation substitutions because of the greater covalency of metal–nitride bonds. Hence, nitride-doping is a more benign method for doping metal oxides without suppressing electronic transitions. [ABSTRACT FROM AUTHOR]

A simple crossover from two-dimensional to three-dimensional correlated disorder of O and N atoms on a cubic lattice has been discovered within the Ba1−xSrxTaO2N series of perovskite oxynitrides. The crossover is driven by lattice expansion as x decreases, and provides a rapid increase in entropy due to a change from subextensive to extensive configurational entropy regimes. [ABSTRACT FROM AUTHOR]

The new compounds LaSrSiO3N and LaBaSiO3N activated with Eu2+ are orange-red light-emitting luminescent materials under excitation in the UV-blue range. They represent the first examples of stoichiometric alkaline earth oxynitridosilicates with a β-K2SO4 structure. The isostructural compound LaEuSiO3N is ferromagnetic with a Curie temperature of 3 K and also shows red luminescence (λmax = 705 nm) under excitation at 405 nm. [ABSTRACT FROM AUTHOR]

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]

Transition-metal oxynitrides with perovskite-type structures are an emerging class of materials with optical, photocatalytic, dielectric and magnetoresistive properties that may be sensitive to oxide-nitride order, but the anion-ordering principles were unclear. Here we report an investigation of the representative compounds SrMO2N (M = Nb, Ta) using neutron and electron diffraction. This revealed a robust 1O/2(O0.5N0.5) partial anion order (up to at least 750 °C in the apparently cubic high-temperature phases) that directs the rotations of MO4N2 octahedra in the room-temperature superstructure. The anion distribution is consistent with local cis-ordering of the two nitrides in each octahedron driven by covalency, which results in disordered zigzag M-N chains in planes within the perovskite lattice. Local structures for the full range of oxynitride perovskites are predicted and a future challenge is to tune properties by controlling the order and dimensionality of the anion chains and networks. [ABSTRACT FROM AUTHOR]

The correlated anion order in the oxynitride perovskite NdVO2N, where disordered zig-zag VN chains segregate into planes within a pseudo-cubic lattice, is similar to that in materials such as SrTaO2N containing d0 transition metal cations. However, NdVO2N has 3d1 V4+ cations and the 3d-electrons are itinerant, showing that the anion chain order in oxynitride perovskites is robust to electron-doping. [ABSTRACT FROM AUTHOR]

Pauling's second crystal rule is shown to be able to predict in a general and simple way the distribution of anions in mixed oxyanion systems such as oxynitrides and oxyhalides with diverse compositions and structure types. 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. [ABSTRACT FROM AUTHOR]

The crystal structure of the n = 1 member of the Ruddlesden-Popper family (SrO)(SrNbO2N)n was refined by the Rietveld method using neutron powder diffraction data. This complex crystallizes in the l4/mmm space group with cell parameters a = 4.0506(2) and c = 12.5936(9) Å. The refined composition was Sr2NbO3.28N0.72, which corresponds to a formal oxidation state for Nb of +4.72, meaning 72% Nb(V) and 28% Nb(IV). The nitrogen atoms order in the equatorial sites of the niobium octahedra according to Pauling's second crystal rule as the more charged anion occupies the site showing the larger bond strength sums. Pauling's second crystal rule is shown to be able to predict the distribution of anions in the available crystallographic sites in other mixed anion systems such as oxyhalides with K2NiF4 structures and other oxynitrides. The defect structure of the n = 1 and n = 2 members of the same family was investigated by high-resolution electron microscopy. Recurrent intergrowth along the c axis with other Ruddlesden-Popper members (n = 3, 4, and perovskite) is observed, resulting in streaking along this direction in the corresponding electron diffraction patterns. [ABSTRACT FROM AUTHOR]

New oxynitrides of RZrO2N (R = Pr, Nd, and Sm) have been synthesized via a direct solid-state reaction of R2O3 with Zr2ON2 at 1200-1500° 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) Å, b = 8.1707(1) Å, and c = 5.7093(1) A for NdZrO2N] and the structural distortion increases with decreasing R3+ ionic radius. This method may enable new mixed-metal oxynitrides to be synthesized without the use of nitriding gas atmospheres. [ABSTRACT FROM AUTHOR]

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.