Sustainable inorganic pigments with high near-infra-red reflectance based on Fe3+ doped YAlO3 for high temperature applications

Non-toxic inorganic pigments based on the Fe(III)-doped YAlO3 with high near-infra-red (NIR) reflectance were synthesized by a modified Pechini method at 1200 °C. A complete solid solution in the YAl1−xFexO3 system (0 ≤x ≤ 1) was prepared, yielding a wide range of colourations from yellow to red, depending on the iron content. Good pigment stability was achieved in a commercial high temperature glaze, used in the ceramic industry to colour glazes on tiles. The pieces coated with the pigmented glazes reached NIR solar reflectance values between 43% and 32%. The temperature protection studies carried out with the glazes pigmented with YAl0.75Fe0.25O3 and YFeO3 compositions, conclude that the pigmented samples reduce the temperature of a building by 5 °C and 4 °C, respectively, in comparison to the unpigmented glaze. Thus, these pigments can be excellent candidates for used in high-temperature applications such as colouring ceramic high temperatures glazes, as well as cool pigments in walls or roofs of buildings.Funding for open access charge: CRUE-Universitat Jaume

The unexplored δ-phase of KY3F10: toward novel Eu3+-doped nanoplates with a ‘super-diamond’ structure for optical applications

This article describes a new, simple, and high-yield method based on a sonochemical process for obtaining the δ-KY3F10·xH2O compound with a ‘super-diamond’ structure, a material that has been completely neglected in the literature since it was first discovered. We explore the mechanism underlying the formation of the synthesized nanomaterials and show their connection with the pH of the medium. Additionally, we demonstrate for the first time the adequacy of the δ-phase of KY3F10 for optical applications through the novel Eu3+-doped nanoplates, which exhibit long lifetimes and high quantum efficiencies. The results reveal that this material, which also has zeolitic characteristics, can have a strong impact on future photonic and associated applications

Unraveling the superior role of dicarboxylic acids as surface chelators in Eu3+-doped yttrium fluorides: A systematic modulation of the crystal phases and morphologies for highly tuned optical performance

Eu3+-doped YF3 and KY3F10 phosphors have been prepared hydrothermally in a wide range of pH values without the use of surface chelators and adding oxalic or tartaric acid. We have proved, for the first time, the usefulness of dicarboxylic acids to modulate the evolution of the surface and crystal phases in the KF-YF3 system. The morphologies and crystal structures of the materials displayed a critical dependence on the pH and the chelator employed, and a plausible mechanism to explain the differences among the distinct series of samples is proposed. As a result, the fluorides exhibited outstanding and tunable photoluminescence, with extremely high quantum efficiencies and very long lifetimes. The asymmetry ratio and Judd-Ofelt parameters calculations allowed us to establish a relationship between the optical performance of the compounds and their physicochemical properties. We feel that this study can arouse widespread interest within the materials engineering community, since similar procedures could be implemented to the extended family of complex yttrium/lanthanide fluorides for advanced applications in important fields such as bioanalytics, biomedics, or photonics. Indeed, the materials in the present work, with orangish-yellow colored emissions, could be very interesting for application in white light emitting diodes through their combination with blue chips

Practical guidance for easily interpreting the emission and physicochemical parameters of Eu3+ in solid-state hosts

Materials doped with the luminescent Eu3+ ion are attracting an ever-increasing amount of attention due to their potential applications in solid-state lighting, display devices, solar cells, or bioanalytics. But, why Eu3+? Unlike other lanthanides, its electronic features make the calculation of some physicochemical parameters quite straightforward, since they can be extracted directly from the emission spectrum. Highly appreciated for its reddish emission, the luminescent ion has also been widely used as a site-sensitive structural probe. With this in mind, this paper aims to offer easy guidance with helpful advice on how to interpret measurements of the emission spectra. It also presents the most useful tools for saving time, and gives a focused and practical explanation of the theoretical concepts involved.Funding for open access charge: CRUE-Universitat Jaume

Environmental-friendly yellow pigment based on Tb and M (M = Ca or Ba) co-doped Y2O3

A yellow inorganic ceramic pigment with general formula Y1.86−xMxTb0.14O3−x/2 (M = Ca and/or Zn) with x = 0.06, 0.32 and 0.64 were synthesized by a modified Pechini method. XRD, SEM and HRTEM/EDX analysis showed the formation of solid solution at 1300 °C when x = 0.06 and 0.32. The best b* yellow coordinates were obtained for Ca and Zn co-doped Y1.86Tb0.14O3 samples. The intensity of the yellow colour in the samples is related to the presence of Tb4+ ions. Samples with higher concentration of Tb4+ ions lead to a better yellow colour. The chemical stability of these pigments was determinate in an industrial glaze. The glazing tests indicated that the powder samples with x = 0.06 and 0.32 fired at 1300 °C were stable in the glaze. These results make it a potential candidate for environmental friendly yellow ceramic pigment to be used in applications such as pigment for glazes or inkjet printers.We thank the “Bancaja-Universitat Jaume I” – project No. P1 1B2011-25 (MP, HB, EC) for financial support. We also thank to the SCIC “Servicios Centrales de Instrumentación Científica” and ITC “Instituto de Tecnología Cerámica” of the Jaume I University for the facilities in the different techniques. VDL thanks “Ministerio de Ciencia e Innovación” for the research contract

New insights on the structural and optical properties of Ce–Ti mixed oxide nanoparticles doped with praseodymium

Nanostructured, doped Ce–Ti mixed oxides are potential materials for several applications such as pigments, catalysis, fuel cells, optical films, and gas sensors. In this article, a series of Pr-doped Ce–Ti oxides have been prepared by the solvothermal method. These compounds were characterized by XRD, Raman, N2 sorption, SEM and UV–VIS spectrophotometry techniques. The experimental results suggest that spherical morphology, nanocrystalline particles and high specific surface area (up to 180 m2 g-1) are achieved at low temperature with this free surfactant methodology. Under basic conditions, a single phase product is identified at high temperature (1000 ºC), while for acid or neutral conditions, secondary phases appear. Different colored materials, ranging from yellow to red, are obtained by varying the firing temperature, quantity of doping praseodymium and the pH of the reaction. The chemical stability of these oxides was tested in some industrial polymers or glazes

A new series of environment-friendly reddish inorganic pigments based on AFeO3 (A = Ln, Y) with high NIR solar reflectance

Environment-friendly pigments based onAFeO3(A¼La, Pr, Nd, Sm, Gd, Tb, Y or Yb) with high near-infrared (NIR) reflectance were synthesised by a coprecipitation method at 1200 C. The Rietveldrefinement analysis showed single-phase orthorhombic perovskite for all compositions. All pigments,which showed reddish hues, offered good colour stability after mixing these pigments in powder formwith siloxane transparent paint and two different glazes. The powderepaint mixtures produced withGdFeO3, TbFeO3and YFeO3pigments have the highest NIR solar reflectance, reaching values ofR¼50%.The temperature shielding studies conducted using TbFeO3pigmentepaint mixture for a roof coatingyielded a reduction of 3.2 C in comparison to a commercial pigment. Moreover, the glazes that werepigmented using GdFeO3, TbFeO3and YFeO3compositions also presented the most intense reddishcolours. A study of the thermal and chemical stability of the pigment with the highest NIR solarreflectance showed good stability in both cases. The reddish pigments that were prepared can thereforebe good candidates for use in different applications such as cool pigments or pigments for ceramic glazesat high temperatures

The influence of Ca2+ and Zn2+ doping on the development of sustainable pigments based on GdFeO3 perovskite: From a reddish colour towards a pure black

Black pigments are very commonly used and arouse widespread interest in the ceramic industry. Nevertheless, these pigments contain toxic elements that are detrimental to human health. In view of this, the present work is focused on the development of sustainable black pigments prepared by a coprecipitation method at 1200 °C. Samples with the nominal formula (Gd1–xCax)(Fe0.95Zn0.05)O2.975–x/2 (x = 0.00, 0.05, 0.10) showed single-phase orthorhombic perovskite. The presence of dopants played an important role in the reduction of Fe3+ to Fe2+ and caused different local distortions in the structure which explained the final black colouration of these pigments in comparison with the red GdFeO3 sample. The loss of symmetry and the increase in the number of d-d transitions of iron may explain the aforementioned changes. Co-doped pigments reached low C* values, improving on the purest black colour obtained in a commercial black ceramic pigment, which contains toxic elements. In addition to presenting good NIR solar reflectance values of up to 8%, the final colours of these pigments were also stable after their application in a commercial transparent glaze at 1080 °C that could be used for tiles.Funding for open access charge: CRUE-Universitat Jaume

Enhanced conductivity and nonlinear voltage–current characteristics of nonstoichiometric BaTiO3 ceramics

The electrical conductivity of both BaO-deficient and TiO2-deficient BaTiO3 ceramics shows nonohmic, low-field characteristics at temperatures >∼200°C in contrast to stoichiometric BaTiO3 for which the electrical conductivity is independent of applied voltage. The nonlinearity is observed in both bulk and grain-boundary resistances of ceramics that are both porous (∼82%) and nonporous (∼98%) and is not associated with interfacial phenomena such as Schottky barriers and memristors or with charge injection from the electrodes. Results, shown as a function of time over the temperature range 200°–750°C with field gradients in the range ∼0.5–20 V/mm, indicate that an excited state is reached that is time, temperature, and field dependent. This effect appears to be caused by departures from local electroneutrality in the defect structure of nonstoichiometric BaTiO3 which are reduced by electron transfer on application of a dc bias, leading to a more conducting, low-level excited state in which holes associated with underbonded oxygens, presumably as O− ions, are the principal charge carriers. Ceramics gradually return to their ground state in two stages on removal of the dc bias and the conductivity decreases overall by two to three orders of magnitude

Phase transition hysteresis and anomalous Curie-Weis behavior of ferroelectric tetragonaltungsten bronzes Ba2RETi2Nb3O15:RE=Nd, Sm

The ferroelectric tetragonal tungsten bronze TTB phases, Ba2RETi2Nb3O15 :RE=Nd,Sm, were prepared by low temperature solvothermal synthesis. The permittivity versus temperature data of sintered ceramics show two unusual features: first, a hysteresis of 50–100 °C between values of the Curie temperature Tc on heat-cool cycles and second: a huge depression in the Curie–Weiss temperature T0. Both effects are attributed to the complex nature of their TTB-related crystal structures with different superstructures above and below Tc and the difficulty in nucleating ferroelectric domains on cooling through Tc. Several factors may contribute to the latter difficulty: first, the structures contain two sets of crystallographic sites for the “active” Ti, Nb ions; second, the distribution of Ti and Nb over these two sets of sites is not random but partially ordered; and third, below Tc a weak commensurate superstructure perpendicular to the polar c axis is present, but above Tc a weak incommensurate superstructure in a similar orientation is present. Hence the formation of the ferroelectric structure on cooling requires both nucleation of polar domains involving two sets of cation sites and structural change from an incommensurate to a commensurate supercel