Tetragonal tungsten bronzes (TTBs), an important class of oxides known to exhibit ferroelectricity, undergo complex distortions, including rotations of oxygen octahedra, which give rise to either ...incommensurately or commensurately modulated superstructures. Many TTBs display broad, frequency-dependent relaxor dielectric behavior rather than sharper frequency-independent normal ferroelectric anomalies, but the exact reasons that favor a particular type of dielectric response for a given composition remain unclear. In this contribution the influence of incommensurate/commensurate displacive modulations on the onset of relaxor/ferroelectric behavior in TTBs is assessed in the context of basic crystal-chemical factors, such as positional disorder, ionic radii and polarizabilities, and point defects. We present a predictive crystal-chemical model that rationalizes composition–structure–properties relations for a broad range of TTB systems.
The increasing awareness of the environmental and health threats of lead as well as environmental legislation, both in the EU and around the world targeted at decreasing the use of hazardous ...substances in electrical appliances and products has reinvigorated the race to develop lead-free alternatives to lead zirconate titanate (PZT), which presently dominates the market for piezoelectric materials. Emphasis has been placed on one of the most likely piezoelectric materials, potassium sodium niobate (KNN), as a lead-free replacement for PZT. KNN has been speculated to have better environmental credentials and is considered as a "greener" replacement to PZT. However, a comparative environmental impact assessment of the life cycle phases of KNN versus PZT piezoelectric materials has not been carried out. Such a life cycle assessment is crucial before any valid claims of "greenness" or environmental viability of one material over the other can be made and is the focus of this paper. Against this backdrop, a methodologically robust life cycle supply chain assessment based on integrated hybrid life cycle framework is undertaken within the context of the two piezoelectric materials. Results show that the presence of niobium in KNN constitutes far greater impact across all the 16 categories considered in comparison with PZT. The increased environmental impact of KNN occurs in the early stages of the LCA due to raw material extraction and processing. As a result, the environmental damage has already occurred before its use in piezoelectric applications during which it doesn't constitute any threat. As such, the use of the term "environmentally friendly" for the description of KNN should be avoided. Cost-benefit analysis of substituting PZT with KNN also indicates that the initial cost of conversion to KNN is greater, especially for energy usage during production. This environmental assessment has allowed us to define and address environmental health and safety as well as sustainability issues that are essential for future development of these materials. Overall, this work demonstrates insightful findings that can be garnered through the application of life cycle assessment and supply chain management to a strategic engineering question which allows industries and policy makers to make informed decisions regarding the environmental consequences of substitute materials, designs, fabrication processes and usage.
Bi
(1−
x
)
RE
x
FeO
3
(BREF100x, RE = La, Nd, Sm, Gd) has been investigated with a view to establish a broad overview of their crystal chemistry and domain structure. For
x
≤ 0.1, the perovskite ...phase in all compositions could be indexed according to the rhombohedral, R3c cell of BiFeO
3
. For Nd and Sm doped compositions with 0.1 <
x
≤ 0.2 and
x
= 0.15, respectively, a new antipolar phase was stabilised similar in structure to PbZrO
3
. The orthoferrite, Pnma structure was present for
x
> 0.1,
x
> 0.15, and
x
> 0.2 in Gd, Sm, and Nd doped BiFeO
3
, respectively. For
x
> 0.2, La doped compositions became pseudocubic at room temperatures but high angle XRD peaks were broad and asymmetric. These compositions have been indexed as the orthoferrite structure. It was concluded therefore that the orthoferrite phase appeared at lower values of
x
as the RE ferrite, end member tolerance factor decreased. However, the compositional window over which the PbZrO
3
-like phase was stable increased with increasing end member tolerance factor but was not found as single phase in La doped compositions at room temperature. On heating, the PbZrO
3
-like phase in BNF20 transformed to the orthoferrite, Pnma structure.
T
C
for all compositions decreased with decreasing A-site, average ionic polarizabilty and tolerance factor. For compositions with R3c symmetry, superstructure and orientational, and translational (antiphase) domains were observed in a manner typical of an antiphase-tilted, ferroelectric perovskite. For the new PbZrO
3
-like phase orientational domains were observed.
Nanoscale and mesoscopic disorder and associated local hysteretic responses underpin the unique properties of spin and cluster glasses, phase-separated oxides, polycrystalline ferroelectrics, and ...ferromagnets alike. Despite the rich history of the field, the relationship between the statistical descriptors of hysteresis behavior such as Preisach density, and micro and nanostructure has remained elusive. By using polycrystalline ferroelectric capacitors as a model system, we now report quantitative nonlinearity measurements in 0.025-1 μm³ volumes, approximately 10⁶ times smaller than previously possible. We discover that the onset of nonlinear behavior with thickness proceeds through formation and increase of areal density of micron-scale regions with large nonlinear response embedded in a more weakly nonlinear matrix. This observation indicates that large-scale collective domain wall dynamics, as opposed to motion of noninteracting walls, underpins Rayleigh behavior in disordered ferroelectrics. The measurements provide evidence for the existence and extent of the domain avalanches in ferroelectric materials, forcing us to rethink 100-year old paradigms.
Ti3SiC2 was deposited onto titanium substrates using electrophoretic deposition; a 4.3 wt% suspension of Ti3SiC2 in water at pH 9 was used with 10 V field applied across the substrates. After 10 min ...of deposition, the coating surface density was 1.89 ± 0.26 mg/cm2. The thin coatings were then rapidly densified using a Renishaw AM250 3D printing laser to scan the surface. Cross sections of the substrate post sintering, showed the coating thickness to be 10–30 μm and densified with silicon loss constrained to the surface, although the overall coverage and adhesion varies. Preliminary Raman spectroscopy results suggest some MAX phase remains after sintering, but further characterisation is required to confirm.
•1.89 ± 0.26 mg/cm2 green coatings of Ti3SiC2 deposited on titanium via EPD•10–30 μm coating bands with varying adhesion achieved via laser densification•Raman indicates some Ti3SiC2 present in sintered coating.
Temperature‐stable, medium‐permittivity dielectric ceramics have been used as resonators in filters for microwave (MW) communications for several decades. The growth of the mobile phone market in the ...1990s led to extensive research and development in this area. The main driving forces were the greater utilization of available bandwidth, that necessitates extremely low dielectric loss (high‐quality factor), an increase in permittivity so that smaller components could be fabricated, and, as ever in the commercial world, cost reduction. Over the last decade, a clear picture has emerged of the principal factors, that influence MW properties. This article reviews these basic principles and gives examples of where they have been used to control microwave properties and ultimately develop new materials.
The development of oxides with high figure of merit, ZT, at modest temperatures (∼300–500 °C) is desirable for ceramic-based thermoelectric generator technology. Although ZT is a compound metric with ...contributions from thermal conductivity (κ), Seebeck coefficient (S), and electrical conductivity (σ), it has been empirically demonstrated that the key to developing thermoelectric n-type oxides is to optimize σ of the ceramic to ∼1000 S/cm at the operating temperature. Titanate-based perovskites are a popular choice for the development of n-type oxide ceramics; however, the levels of σ required cannot be achieved without control of the ceramic quality, significant reduction of the ceramic in low P(O2) atmosphere (e.g., N2/5%H2), and the use of specific dopants and dopant mechanisms, which allow the egress of oxygen homogeneously from the lattice. Here, we discuss the processing protocols to fabricate reliable, reproducible ceramic oxides and schemes for inducing high levels of σ, thereby optimizing the power factor (PF = σS 2) and ZT. The problems associated with measuring κ, σ, and S to achieve reproducible and accurate values of ZT are discussed, as are future directions which should enable further optimization. Finally, we comment on how these protocols may be applied to other systems and structures.
Neutron powder diffraction was used to determine changes in the nuclear and magnetic structures of Bi1−x Nd x FeO3 polymorphs involved in the first-order displacive phase transitions from the ...high-temperature nonpolar phase to the low temperature polar (x ≤ 0.125) and antipolar (0.125 ≤ x ≤ 0.25) phases, respectively. The high-temperature phase (O 1), which crystallizes with a structure similar to the room-temperature form of NdFeO3, exhibits Pbnm symmetry and unit cell √2a c × √2a c × 2a c (where a c ≈ 4 Å is the lattice parameter of an ideal cubic perovskite), determined by a − a − c + octahedral tilting. The low-temperature polar structure (R) is similar to the β-phase of BiFeO3 and features rhombohedral symmetry determined by a − a − a − octahedral rotations and cation displacements. The recently discovered antipolar phase (O 2) resembles the antiferroelectric Pbam (√2a c × 2√2a c × 2a c) structure of PbZrO3 but with additional displacements that double the PbZrO3 unit cell along the c-axis to √2a c × 2√2a c × 4a c and yield Pbnm symmetry. The O 1 ↔ R and O 1 ↔ O 2 transitions are both accompanied by a large discontinuous expansion of the lattice volume in the low-temperature structures with a contrasting contraction of the FeO6 octahedral volume and an abrupt decrease in the magnitude of octahedral rotations. The O 1 ↔ O 2 transition, which occurs in the magnetic state, is accompanied by an abrupt ≈90° reorientation of the magnetic dipoles. This coupling between the nuclear and magnetic structures is manifested in a significant magnetization anomaly. Below 50 K, reverse rotation of magnetic dipoles back to the original orientations in the high-temperature O 1 structure is observed.
Solar cells are considered as one of the prominent sources of renewable energy suitable for large-scale adoption in a carbon-constrained world and can contribute to reduced reliance on energy ...imports, whilst improving the security of energy supply. A new arrival in the family of solar cells technologies is the organic-inorganic halide perovskite. The major thrust for endorsing these new solar cells pertains to their potential as an economically and environmentally viable option to traditional silicon-based technology. To verify this assertion, this paper presents a critical review of some existing photovoltaic (PV) technologies in comparison with perovskite-structured solar cells (PSCs), including material and performance parameters, production processes and manufacturing complexity, economics, key technological challenges for further developments and current research efforts. At present, there is limited environmental assessment of PSCs and consequently, a methodologically robust and environmentally expansive lifecycle supply chain assessment of two types of PSC modules A and B is also undertaken within the context of other PV technologies, to assess their potential for environmentally friendly innovation in the energy sector. Module A is based on MAPbX3 perovskite structure while module B is based on CsFAPbX3 with improved stability, reproducibility and high performance efficiency. The main outcomes, presented along with sensitivity analysis, show that PSCs offer more environmentally friendly and sustainable option, with the least energy payback period, as compared to other PV technologies. The review and analysis presented provide valuable insight and guidance in identifying pathways and windows of opportunity for future PV designs towards cleaner and sustainable energy production.
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