New Red‐Shade Ceramic Pigments Based on Y₂Sn_2−xCr_xO_7−δ Pyrochlore Solid Solutions

Abstract

New high-stability red-shade ceramic pigments based on pyrochlore solid solutions Y 2 Sn 2؊x Cr x O 7؊␦ (x ‫؍‬ 0 -1, 0 < ␦ ‫؍‬ 0 -1 ⁄2x) were developed employing conventional solid-state reaction synthesis. The relationship between their optical properties and microstructure was analyzed by X-ray diffractometry and ultraviolet-visible-light spectroscopy. Decomposition of the structure with formation of the perovskite YCrO 3 observed for chromium substitutions x > 5 was attributed mainly to high concentration of defects. The structural and optical parameters of the materials were found to correlate with the concentration of a species with higher oxidation state than Cr(III), such as Cr(IV) or Cr(V).

Anti-site disorder and physical properties in microwave synthesized RE2Ti2O7 (RE = Gd, Ho) pyrochlores

“…[17][18][19] Here in this work we demonstrate that the microwave (MW) -assisted method produces off-equilibrium (metastable) pyrochlore-type phases with varying amounts of anti-site defects, in agreement with other more recently developed alternative synthesis methods, e.g. [20][21][22] In the last decades several alternative routes have been proposed such as microwave (MW) synthesis, molten salt mediated synthesis, co-precipitation of hydroxides, sol-gel and citrate based methods, and mechanical milling, where the time and temperature requirements for synthesis are significantly reduced. 19 Traditionally, RE 2 Ti 2 O 7 compounds are prepared by solid state reactions, which require repeated and long synthesis procedures at temperatures of up to ≈ 1400 ºC and intensive grinding at the initial and intermediate stages of processing to achieve single phase material.…”

Preparation through Aerosols of Cr‐Doped Y2Sn2O7 (Pyrochlore) Red‐Shade Pigments and Determination of the Cr Oxidation State

“…2 Among those showing the highest red hue is Cr-doped yttrium-tin pyrochlore (Y 2 Sn 2 O 7 ), which possesses the chemical and thermal stability required for high-temperature applications. 3 The preparation of this pigment has been previously conducted by using only the traditional ceramic method, which involves homogenization by milling of the mixture of the corresponding metal oxides, its calcination at very high temperature (1400°C) to develop the desired crystalline phase, and a final milling process to reduce and homogenize particle size. 3 To decrease this synthesis temperature, the addition of some mineralizers to the starting mixture has been successfully assayed (1100°C), 3 although the use of these flux agents also causes some undesired environmental effects related to the emission of pollutants to the atmosphere.…”

Synthesis by pyrolysis of aerosols and ceramic application of Cr-doped CaYAlO4 red–orange pigments

“…For example, it is remarkable the important research effort carried out during the last years to find new red pigments to replace those commercially used since most of them are toxic. [1][2][3][4][5] YCaAlO 4 belongs to the series of A 3+ B 2+ AlO 4 aluminates (A 3+ = Y, Nd, La; B 2+ = Ca, Sr), which crystallize in the K 2 NiF 4 type structure consisting of a 1/1 intergrowth of ABO 3 perovskite and AO rock-salt (NaCl) type layers connected by anisotropic A-O apical -B bridge bonds, where A and B elements present ninefold coordination whereas Al is octahedrally coordinated. 6,7 These complex oxides are versatile compounds which, when doped with different transition elements, result in materials with interesting electric, magnetic, [8][9][10] optical 11 and infrared 6 properties.…”