Pyrochlore Phase Research Articles

Optical temperature sensing characteristics of Gd2Ti2O7: Sm3+, Tm3+ phosphors

In this experiment, Gd2Ti2O7: x% Sm3+, 1% Tm3+ (x = 0.1, 0.3, 0.5, 1) optical temperature sensing materials were created with the hydrothermal method, with urea used as the precipitant. The X-ray diffraction (XRD) analysis results showed that the samples we prepared had a face-centered cubic phase pyrochlore structure. As the field emission scanning electron microscope (FE-SEM) images illustrated, the morphology of the samples was irregularly spherical. Furthermore, by measuring the temperature-dependent emission spectrum of each sample, it was discovered that the Tm3+ had a significant thermal quenching phenomenon, while the Sm3+ had a slower thermal quenching trend, so their fluorescence intensity ratios (FIRs) varied significantly with the temperature. This variation could be used to represent the temperature. By comparing different samples, we found that the Sm3+ concentration rose and the absolute sensitivity of the samples rose gradually, while the relative sensitivity gradually became smaller and smaller. The maximal absolute sensitivity was 0.0686 K−1 (483 K, 1% Sm3+, 1% Tm3+), and the maximal relative sensitivity was 3.1% K−1 (297.7 K, 0.1% Sm3+, 1% Tm3+). At the same time, through observation, it was determined that the luminescence color of the Gd2Ti2O7: 0.1% Sm3+, 1% Tm3+ phosphors varied from blue to orange-red continuously when the temperature gradually increased. We could roughly estimate the temperature change by the luminescence color. The test of the temperature cycle showed that the repeatability of temperature measurement using FIR was good. Overall, the Gd2Ti2O7: Sm3+, Tm3+ phosphors had good application prospects.

Development and characterization of a novel Y-Ti-O based aluminum nano-composite processed by high energy ball-milling and spark plasma sintering

The present work reports synthesis and characterization of bulk Y 2 Ti 2 O 7 ‑aluminum nano-composites processed by high energy ball-milling followed by spark plasma sintering. Y-Ti-O based particles were synthesized by mechanical alloying (MA) a 1:2 stoichiometric mixture of Yttrium Oxide (Y 2 O 3 ) and Titanium Oxide (TiO 2 ), and further calcinating the ball-milled mixture at different temperatures. The calcinated powder was further ball-milled for different durations to fabricate the nanoparticles. The X-Ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) and Raman spectroscopy confirmed the formation of stable Y 2 Ti 2 O 7 . The XRD and Scanning Electron Microscope (SEM) of ball-milled powder reveal crystallite size and particle size of 5 nm and 30 nm, respectively. The XRD data indicates that prolonged ball-milling duration does not deteriorate the structural integrity of the Y 2 Ti 2 O 7 phase. The nano-dispersoids were reinforced in aluminum matrix to obtain dispersion strengthening. The compressive yield strength increased from 60 to 390 MPa by introducing 1 Wt% Y 2 Ti 2 O 7 . • Y 2 Ti 2 O 7 pyrochlore phase was successfully synthesized by ball milling & calcination. • Further ball-milling of calcinated powder has produced Y 2 Ti 2 O 7 nanoparticles of 30 nm. • Prolonged ball milling does not destabilize structural integrity of pyrochlore phase. • Seven times increase in yield strength is observed in Al-Y 2 Ti 2 O 7 nanocomposite.

A study of phase evolution of Fe-doped bismuth tantalate pyrochlore

The phase formation process of Bi2FeTa2O9.5 (sp. gr. Fd-3m) synthesized by traditional ceramic technology was studied. Bismuth orthotantalate BiTaO4 (sp. gr. Pnna) was found to be the precursor of the pyrochlore phase. The high-temperature synthesis of the iron-containing pyrochlore and the formation of a characteristic dendrite-like microstructure took place at temperatures above 900°С. The pure pyrochlore was obtained at a temperature of 1050°С. At the early stages of calcination, at a temperature close to 650 °C, the main part of iron (III) oxide, as a precursor, interacts with bismuth tantalate, and at temperatures above 950 °C, no Fe2O3 traces in the sample were found. Complex oxides Bi25FeO40 (sp. gr. I23), Bi3TaO7 (sp. gr. Fm-3m) were found as intermediate phases during the synthesis of pyrochlore. Pyrochlore of the given composition Bi2FeTa2O9.5 had a porous microstructure with a grain size of 0.5–1.0 μm. The calcination temperature did not significantly affect the microstructure of the sample. The porosity of synthesized samples with a pyrochlore structure does not exceed 21%.

Pyrochlore-like ZrO2-PrOx compounds: The role of the processing atmosphere in the stoichiometry, microstructure and oxidation state

The object of this work is to study the relation between composition, microstructure and oxidation state of Pr2±xZr2∓xO7±y materials produced by the laser–floating zone (LFZ) technique. Three compositions are studied, nominally Pr1.7Zr2.3O7+y, Pr2Zr2O7+y and Pr2.24Zr1.76O7±y, all within the pyrochlore field in the ZrO2–PrOx phase diagram. Samples have been processed under four different atmospheres (O2, air, N2 and 5%H2(Ar)), so as to vary the environmental conditions from oxidising to reducing. Sample colouration ranged from dark brown to bright green, owing to varying Pr4+ content. A close correlation is found between the phase homogeneity, the microstructure and the Pr content. Pr–deficient samples present a homogeneous microstructural aspect and composition, whereas Pr–rich compositions always break into 5–25 µm–sized grains with pyrochlore phases at the grain centre and ill–crystallised, Pr–rich oxidised phases at the grain–boundaries. Raman spectroscopy shows that different types of oxygen disorder occur depending on composition and processing atmosphere: in Pr–poor samples oxygen interstitials are created to compensate for Zr4+ excess charge, whereas in Pr–rich samples oxygen disorder occurs around the Pr3+ or Pr4+ ions substituting for Zr4+, because of size–mismatch. Magnetic measurements showed a high Pr4+ content, which has been attributed to several factors: the highly oxidised state of the feedstock material, the segregation of Pr and O–rich grain boundaries in compositions with praseodymium molar rate> 0.5, and the lower oxide–ion conductivity for PZO compositions, compared to either Pr–poor or Pr–rich compositions. Post–processing thermal annealing in a vacuum at 1000 °C enabled total Pr reduction, with the exception of the Pr–rich P2.24 samples, where some Pr4+ ions remained in the oxidised state.

(Invited) Electrocatalysts of Complex Oxides for Water Splitting

Low temperature electrolysis plays a critical role in our effort for energy generation with net zero or negative carbon impacts. This process produces green hydrogen through catalytic splitting of water and requires the development of highly active and, perhaps more importantly, highly stable electrocatalysts for oxygen evolution reaction (OER). This presentation will focus on examining the structure-property relationship of complex oxides that are made of AxByOz, where A and B can be a single metal cation or mixed cations, respectively. Depending the compositions, perovskite, pyrochlore, and Ruddlesden-Popper (RP) phase solids all have been found to be highly active for OER in either acid or base conditions. Noticeably, structurally defective solid catalysts such as those observed in defect perovskite (J. Am. Chem. Soc., 2014, 136, 14646-14649) often possess high activity. I will review some of the latest advancements in understanding the mechanisms of OER and discuss the new results on regulating the cation sites and oxygen defect chemistry for enhancing the bond-stability of key catalytic constituents and surface structures for OER performance.

Properties of lanthanide containing Aurivillius phases Ln2Bi3FeTi3O15 (Ln = La, Pr, Nd, Sm, Gd)

The phase formation in the series Ln2Bi3FeTi3O15 (Ln = La, Pr, Nd, Sm, Gd) was studied. It was found that the layered perovskite structure was formed after annealing at 1000 °C. Further increase in the synthesis temperature to 1100 °C did not affect the phase composition, excluding Gd-containing sample, where perovskite structure was partially destroyed to form the pyrochlore phase based on Bi2Ti2O7. Reversible anomalies obtained by differential thermal analysis indicate the phase transitions with a change in the crystal lattice symmetry in case of a perovskite-like phase and a transition of the order-disorder type in case of a pyrochlore structure.

Structure dependence of dielectric properties in Ca-doped bismuth magnesium niobate pyrochlores

The cubic pyrochlore Bi1.5MgNb1.5O7 (BMN) materials have large permittivity, good temperature stability, and extremely low dielectric loss. The structure and dielectric properties of Bi1.5Mg1−xCaxNb1.5O7 (BMCN, x = 0.0–0.5) are discussed systematically. All the samples except x = 0.5 were found that the dominant crystalline phase was cubic pyrochlore structure. The BMN (x = 0.0) cubic pyrochlore phase contained little impurity Mg4Nb2O9. Although Ca-doping inhibited the formation of the impurity phase Mg4Nb2O9, excessive Ca-doping (x ≥ 0.4) led to another second phase CaBi2Nb2O9 in BMCN structure. The substitution of Ca2+ brought about the reduction of structure disorder which were caused by abnormal cell shrinkage. It evidenced that Ca2+ ions are prone to substitute Mg2+ ions on A-site, then take on the B-site when the more Ca2+ ions doping in the pyrochlores. The permittivity of doped BMCN (x = 0.1–0.5) was smaller than that of BMN, and decreased with the increase of Ca2+ doping. The dielectric loss of doped BMCN increased due to the lattice defects caused by larger Ca2+ substitution for Mg2+, and the existence of the second phase with x = 0.4–0.5. The temperature dependence of the dielectric properties become unstable by Ca-doping. The Ca2+ substitution led to a closer association of BO6 octahedra, which had adverse impact on temperature stability of BMCN (x = 0.1–0.3). The coexistence of the second phase with positive temperature coefficient improved the dielectric temperature stability of the BMCN (x = 0.4–0.5). The dielectric loss was interpreted on the basis of the interfacial polarization at the grain-boundary region, which would become sensitive to temperature/frequency.

Tetrabutylammonium hydroxide mediated sol-gel synthesis of samarium titanate to enhance photocatalytic activity

To obtain photocatalytically active materials with increased porosity, tetrabutylammonium hydroxide (TBAOH) was applied to synthesize the samarium titanate. All the Sm2Ti2O7(v) samples have a solely pyrochlore samarium titanate crystal phase, and the crystallite size of Sm2Ti2O7 decreases from 39.1 nm to 19.5 nm with increasing TBAOH volume in the sol. The porosity of the Sm2Ti2O7(v) samples is significantly promoted after using TBAOH, and Sm2Ti2O7(1.0) has the maximum BET surface area of 12.67 m2/g and the maximum pore volume of 0.0271 cm3/g. The bandgap energy for the Sm2Ti2O7 is 3.41 eV, and the bandgap energies for Sm2Ti2O7(0.4), Sm2Ti2O7(1.0) and Sm2Ti2O7(1.4) are 3.61, 3.69 and 3.79 eV, respectively. The Sm2Ti2O7(v) samples can only respond to UV irradiation. Sm2Ti2O7(1.0) has the lowest photoluminescence intensity, indicating the lowest recombination efficiency for the electrons and holes. More Sm2+ exists in Sm2Ti2O7(1.0) prepared using TBAOH. The degradation efficiency of RBR X-3B is drastically enhanced with increasing TBAOH volume, and the maximum degradation efficiency is obtained for Sm2Ti2O7(1.0). The photocatalytic efficiency is 77.1% after 60 min of reaction for Sm2Ti2O7(1.0), and the overall dye removal efficiency is 96.6%. 82.5% of the original activity for Sm2Ti2O7(1.0) is maintained in the fourth reaction cycle.

Phase equilibria in the La2O3-Sm2O3-ZrO2 system: Experimental studies and thermodynamic modeling

A series of ceramic samples were prepared to experimentally investigate sub-solidus phase relations in the La2O3-Sm2O3-ZrO2 system at 1873 K and 1673 K. No ternary compounds have been observed, while the binary La2Zr2O7 and Sm2Zr2O7 pyrochlore phases form a continuous solid solution La2−xSmxZr2O7 in the ternary system at the selected temperatures. X-ray diffraction and microstructure results demonstrated that the pyrochlore phase is stable in the ZrO2-rich corner. The homogeneity range of the pyrochlore phase was carefully determined and the phase boundary of the cubic ZrO2 (fluorite phase) which extends into the ternary system was also constructed via electron probe microanalysis. The as-obtained data were adopted to determine the mixing parameters for the pyrochlore and fluorite phases in the present thermodynamic modeling. A self-consistent database of the La2O3-Sm2O3-ZrO2 system was accordingly established for the first time and the calculations agree well with the experimental data in the current work.

Observation of up conversion/ down conversion luminescence and structural analysis of La2Zr2O7: Pr3+ nano phosphors

Charge transfer band (CTB) transition significantly improves the photoluminescence properties of phosphor materials due to its higher absorption efficiency than the characteristic excitations of rare-earth ions. La2Zr2O7 (LZO): Pr3+ phosphors with varying doping concentrations of Pr3+ were synthesized through the hydrothermal method. The formation of the pure pyrochlore phase was confirmed from powder X-ray diffraction (XRD). The structural analysis was performed from Rietveld refinement of the XRD data. Field emission electron microscope (FESM) equipped with EDX spectroscopy was used to study the surface morphology and elemental compositions. X-ray photoelectron spectroscopy (XPS) analysis of the optimized sample provides the bonding state of the compositions. Under 257 nm CTB excitation, the photoluminescence emission spectra (PL) exhibit all the characteristic emission peaks of Pr3+ ion. The transitions involved in the excitation and emission process have been shown in the energy level diagram of Pr3+ ions. The Concentration quenching effect was explained from Bless relation and Dexter energy transfer theory between activator ions. Decay curves of the prepared phosphors show bi-exponential behavior. The up-conversion emission spectra were recorded under 980 nm laser excitation. The optical transition in the UV–Vis range was investigated based on the diffuse reflectance spectra, and the results match well with the excitation spectra. The photometric study informs the color and the quality of the emitted light. The outcomes produce a new synthesis method to prepare La2Zr2O7:Pr3+ nano phosphor that can be an excellent candidate for solid-state lighting and UV/NIR to the visible converter in solar cell applications.

Pyrochlore Phase in the Bi2O3–Fe2O3–WO3–(H2O) System: its Formation by Hydrothermal-Microwave Synthesis and Optical Properties

Pyrochlore Phase in the Bi2O3–Fe2O3–WO3–(H2O) System: its Formation by Hydrothermal-Microwave Synthesis and Optical Properties

Design and synthesis of high-entropy pyrochlore ceramics based on valence combination

In this paper, we report the design and synthesis of La3+ based high-entropy pyrochlore ceramics (HEPCs) with five different B-site cations using the valence combination strategy. The factors affecting the formation of pyrochlore phase have been investigated. The result reveals that both valence disorder and size disorder can significantly affect the formability of pyrochlore phase, and the formability increases as the two disorders decrease. Following this guideline, a set of new HEPCs with single phase have been successfully synthesized.

Influence of yttrium oxide addition on the characteristics of SnO2 based ceramics

In the presented paper the microstructure and the electrical characteristics of (99.9-x) SnO2 - x Y2O3 - 0.05 Nb2O5 - 0.05 Cr2O3 (mol. %, x = 0, 0.3, 0.5 and 0.7) varistor ceramics in a wide range of current densities 10−9 - 102 A∙cm−2 have been considered. In all samples with Y2O3 addition the SnO2 cassiterite phase with rutile-type structure and Y2Sn2O7 phase with pyrochlore-type structure were observed. The values of the some parameters of ceramics have been calculated and their average values have been found. The lowest shrinkage and average grain size and the highest grain resistivity have the samples with 0.5 mol. % Y2O3 addition. Such ceramics has the largest values of nonlinearity coefficient 48.6, electric breakdown field 14.6 kV∙cm−1, grain boundary breakdown voltage 2.3 V∙barrier−1, activation energy of electrical conduction 0.92 eV and the lowest ones of leakage current 0.09 μA and low-field electrical conductivity 2.9∙10−12 Ohm−1∙cm−1. The simultaneously coordinated changes of structural and electrical parameters of samples prove the barrier mechanism of electrical conductivity in SnO2 - Y2O3 – Nb2O5 - Cr2O3 varistors. The addition of yttrium oxide to tin-oxide ceramics allows increasing the nonlinearity of voltage-current characteristics and considerable decreasing the leakage current of samples. These effects were due to an increase of the amount of yttrium stannate secondary precipitated pyrochlore phase Y2Sn2O7 in ceramics.

Effect of oxygen vacancy on the dielectric relaxation characteristics of PMNT ceramics

The as-sintered 0.68 Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 ceramics were firstly prepared using the Columbite technique and then further annealed in specific atmosphere. The effect of annealing atmospheres, e.g. O2, N2 and air conditions, on the phase structure, microstructure and dielectric properties of ceramics were systematically discussed. The obtained results suggested that, compared to as-sintered sample, there is no obvious difference in phase structure and microstructure for ceramics annealed in O2 atmosphere, showing pure perovskite structure and higher density. While the appearance of second pyrochlore phase and porosity can be found as sample was annealed in nitrogen or air condition. It is worth noting that the dielectric properties of ceramics are very sensitive to the annealing atmosphere and there is a significant increase in dielectric constant and decrease in dielectric loss as the PMNT ceramic was treated in O2 atmosphere, while sample annealed in N2 or air condition would show the opposite trend.

Effect of f–d and d–d Interactions on Dielectric and Optical Properties of Pyrochlore Eu2−xFexTi2O7

X‐ray diffraction, Raman spectroscopy, Fourier‐transform infrared (FTIR) spectroscopy, dielectric property, and UV–vis spectroscopy studies of pyrochlore Eu2−xFexTi2O7 have been performed. The X‐ray pattern shows that Eu2−xFexTi2O7 has a pure pyrochlore phase up to x = 0.2. The structural analysis shows a strong distortion of TiO6 octahedral due to the presence of the interstitial anionic vacant site. A significantly increased band intensity of FTIR spectrum with Fe doping suggests the enhanced anionic disorder in the system. The broadening of Raman peaks with increasing x supports the increased disorder in TiO6 octahedral. Dielectric study of Eu2Ti2O7 shows a diffused dielectric transition below 150 K. The dielectric diffusiveness and transition temperature get enhanced with Fe doping due to enhanced anionic distortion. The dielectric constant of Eu2−xFexTi2O7 is also increased on Fe doping. The UV–vis spectrum exhibits a strong absorbance in the UV region and a redshift with Fe doping. The Tauc plot of UV–vis spectrum shows multiple successive valence band edges and the bandgap gets reduced with Fe doping due to the formation of new interbands. Thus, these materials are interesting for people searching for material to be used in tunable electrical and optical devices.

The Effect of Annealing on the Optoelectronic Properties and Energy State of Amorphous Pyrochlore Y2Ti2O7 Thin Layers by Sol–Gel Synthesis

Pyrochlore titanate (Y2Ti2O7) is a promising material for a wide range of applications in optoelectronics and photocatalysis due to its advantageous chemical, mechanical, and optical properties. To enhance its potential for such uses, however, a high-quality and scalable synthesis method is required. We here investigate the crystallization of sol–gel produced Y2Ti2O7 layers. We observe a transition of the amorphous pyrochlore phase at annealing temperatures below 700 °C. The transmittances of the Y2Ti2O7 thin layers annealed at 400 to 700 °C are approximately 92.3%. The refractive indices and packing densities of Y2Ti2O7 thin layers annealed at 400–700 °C/1 h vary from 1.931 to 1.954 and 0.835 to 0.846, respectively. The optical bandgap energies of Y2Ti2O7 thin layers annealed at 400–700 °C/1 h reduce from 4.356 to 4.319 eV because of the Moss–Burstein effect. These good electronic and optical properties make Y2Ti2O7 thin layers a promising host material for many potential applications.

Eu-Doped Pyrochlore Crystal Nano-Powders as Fluorescent Solid for Fingerprint Visualization and for Anti-Counterfeiting Applications.

Undoped Y2Sn2O7 and Eu3+ doped Y2Sn2O7 samples with doping concentrations 7%, 8%, 9%, and 10% are successfully synthesized by the co-precipitation method. A complete structural, morphological, and spectroscopic characterization is carried out. XRD measurements reveal that samples crystallize in the pure single pyrochlore phase and Eu3+ ions occupy sites with D3d symmetry. After mechanical grinding, the average crystallite size is less than 100 nm for all compositions. Optical characterization shows emission from the 5D0 level towards the lower lying 7F0,1,2,3,4 levels. The CIE color coordinates of all the pyrochlore phosphors are very close to those of the ideal red light. For the visualization of latent fingerprints, different surfaces are tested, including difficult ones (wood and ceramic), with excellent results. All three levels of fingerprint ridge patterns are visualized: core (Level 1), bifurcation and termination (Level 2), and sweat pores (Level 3). Moreover, our nano-powders are used to prepare a stable fluorescent ink.

Dielectric anomalies and structure evolution of annealed (1-x)Pb(Sc1/2Ta1/2)O3-xPb(In1/2Nb1/2)O3 ceramics

The (1-x)Pb(Sc1/2Ta1/2)O3-xPb(In1/2Nb1/2)O3 [(1-x)PST-xPIN] (x = 0.2, 0.4, 0.6, and 0.8) solid-solution ceramics were synthesized by conventional solid-state reaction method. The phase structure, microstructure, and dielectric properties were analysed. In order to obtain various ordering degrees, annealing treatment at 700 °C for 10 h, 20 h, 40 h, and 120 h was conducted on (1-x)PST-xPIN ceramics. The degree of ordering increased significantly with the extension of annealing time in 0.8PST-0.2PIN composition. However, for other compositions, no any superlattice peak was observed at all times of annealing process, which was related to the presence of more pyrochlore phase. In addition to the low-temperature relaxation peaks associated with the disordered arrangement of B-site ions, two new dielectric anomalies were found in the temperature dependence of dielectric constant of annealed (1-x)PST-xPIN solid solution. For annealed 0.8PST-0.2PIN composition, the middle-temperature and high-temperature dielectric anomalies were attributed to the ordered PST region and the incommensurate structure induced by the competition between ordered PST and disordered PST, respectively. The high-temperature dielectric anomalies in 0.6PST-0.4PIN and 0.4PST-0.6PIN compositions originated from the contribution of the ordered PIN region in solid solution. Furthermore, the relatively weak superlattice diffraction spots of (111) were found in selected-area electron diffraction patterns of annealed 0.8PST-0.2PIN ceramic, indicating that the existence of alternately ordering arrangement of B-site ions. Combined with the analysis of element mapping, it was concluded that the annealed (1-x)PST-xPIN solid solution was composed of the ordered PST region, the ordered PIN region, and the disordered region constituted by PST and/or PIN.

21-Component compositionally complex ceramics: Discovery of ultrahigh-entropy weberite and fergusonite phases and a pyrochlore-weberite transition

Two new high-entropy ceramics (HECs) in the weberite and fergusonite structures, along with the unexpected formation of ordered pyrochlore phases with ultrahigh-entropy compositions and an abrupt pyrochlore-weberite transition, are discovered in a 21-component oxide system. While the Gibbs phase rule allows 21 equilibrium phases, 9 out of the 13 compositions examined possess single HEC phases (with ultrahigh ideal configurational entropies: ∼2.7kB per cation or higher on one sublattice in most cases). Notably, (15RE1/15)(Nb1/2Ta1/2)O4 possess a single monoclinic fergusonite (C2/c) phase, and (15RE1/15)3(Nb1/2Ta1/2)1O7 form a single orthorhombic (C2221) weberite phase, where 15RE1/15 represents Sc1/15Y1/15La1/15Pr1/15Nd1/15Sm1/15Eu1/15Gd1/15Tb1/15Dy1/15Ho1/15Er1/15Tm1/15 Yb1/15Lu1/15. Moreover, a series of eight (15RE1/15)2+x(Ti1/4Zr1/4Ce1/4H1/4)2−2x(Nb1/2Ta1/2)xO7 specimens all exhibit single phases, where a pyrochlore-weberite transition occurs within 0.75 < x < 0.8125. This cubic-to-orthorhombic transition does not change the temperature-dependent thermal conductivity appreciably, as the amorphous limit may have already been achieved in the ultrahigh-entropy 21-component oxides. These discoveries expand the diversity and complexity of HECs, towards many-component compositionally complex ceramics (CCCs) and ultrahigh-entropy ceramics.

Cu, Mg Codoped Bismuth Tantalate Pyrochlores: Crystal Structure, XPS Spectra, Thermal Expansion, and Electrical Properties.

The pyrochlore-type solid-solution formation in a Bi1.6Mg0.8-xCuxTa1.6O7.2-Δ system, synthesized for the first time, is observed at x ≤ 0.56. High-temperature X-ray diffraction showed that the pyrochlore phase exists in air up to 1080 °C, where its thermal decomposition leads to the segregation of (Mg,Cu)Ta2O6. The thermal expansion coefficients of the end member, Bi1.6Mg0.24Cu0.56Ta1.6O7.2-Δ, increase from 3.3 × 10-6 °C-1 at room temperature up to 8.7 × 10-6 °C-1 at 930 °C. Rietveld refinement confirmed that the pyrochlore crystal structure is disordered with space group Fd3̅m:2 (Z = 8, no. 227). Doping with copper results in a modest expansion of the cubic unit cell, promotes sintering of the ceramic materials, and induces their red-brown color. X-ray photoelectron spectroscopy demonstrated that the states of Bi(III) and Mg(II) are not affected by doping, and the effective charge of tantalum cations is lower than +5, while the Cu(II) states coexist with Cu(I). The electron spin resonance spectra display a single line with g = 2.2, ascribed to the dipole-broadened Cu2+ signal. The dielectric permittivity of Bi1.6Mg0.8-xCuxTa1.6O7.2-Δ ceramics may achieve up to ∼105, with the dielectric loss tangent varying in the range from 0.2 up to 12. Multiple dielectric relaxations are found at room temperature and above for all samples.