10 Search Results

Barium titanate (BTO) is a lead-free functional ceramic that is widely used in sensors, transducers, and actuators. The increasing demand for complex geometries and quick design iterations motivates the use of additive manufacturing techniques. Laser powder bed fusion (L-PBF) additive manufacturing technique enables the net-shape or near-net-shape fabrication of metals and alloys. Ceramic L-PBF remains challenging due to their high melting temperature. Here, to address this challenge, a nanoparticle ink feedstock was incorporated into the L-PBF process to allow low power melting of BTO. Key print parameters (i.e. laser power, scanning speed, and hatching spacing) were optimized to fabricate millimeter-scalemore » BTO parts. The printed BTO samples possessed an inhomogeneous equiaxed-columnar-cellular microstructure. Semiconducting current-voltage behavior was observed in as-printed samples, which was attributed to the creation of oxygen vacancies. The piezoelectric d₃₃ coefficient was measured to be 4.6 pC/N.« less

In this study, we have investigated the temperature dependence of atomic ordering at multiple length scales in a lead-free sodium niobate-based relaxor, i.e., 0.75 NaNbO₃-0.25 Ba_0.9⁢Ca_0.1⁢TiO₃ (NN-25BCT) via synchrotron x-ray diffraction, Raman spectroscopy, and pair distribution function analysis. High-resolution synchrotron x-ray powder diffraction (SXRD) measurements reveal a ferroelectric phase transition in the relaxor ferroelectric NN-25BCT below the Vogel-Fulcher freezing temperature (𝑇_VF ≈ 270 K). In addition, SXRD analysis demonstrates the competition between in-phase octahedral tilting and ferroelectric order at the long-range scale using mode crystallography. On the other hand, Raman spectroscopic analysis provides evidence of polar ordering for 𝑇 >more » 𝑇_VF (with tetragonal symmetry) persisting up to the Burns temperature (𝑇_B). Furthermore, pair distribution function (PDF) analysis reveals the presence of a polar antiferrodistortive tetragonal phase with 𝑃⁢4⁢𝑏𝑚 space group at short ranges throughout the studied temperatures (i.e., 110 K ≤ 𝑇 ≤500 K), irrespective of nonpolar long-range ordering above 𝑇_VF. Therefore, our measurements provide direct evidence for the presence of polar ordering at short ranges and their gradual transformation into long-range polar ordering using an integrated multiscale structural analysis. In conclusion, as a result of a transition from relaxor to a ferroelectric phase in the vicinity of room temperature, NN-25BCT can be exploited for applications in pyroelectric detectors, electrocaloric devices, and multilayered ceramic capacitors.« less

In the current work, we have performed multiscale structural analysis of a Pb-free sodium niobate-based smart system, i.e., 0.9⁢NaNbO₃ –0.1⁢Ba_0.9⁢Ca_0.1⁢TiO₃ (NN-10BCT) reported earlier for its high ferroelectric response. We have investigated the temperature-dependent evolution of crystal structure at long, medium, and short ranges using synchrotron x-ray diffraction (SXRD), Raman scattering, and pair distribution function(PDF) techniques in conjunction with dielectric studies. Temperature-dependent synchrotron x-ray diffraction data combined with dielectric analysis suggest two unique polymorphic phase boundaries (PPB) with two coexisting ferroelectric phases stable in the wide temperature ranges. These PPBs are stable in different regions viz. (i) cryogenic temperatures with coexistingmore » R3c and Pmc⁢2₁ phases (ii) vicinity of room temperatures with coexisting Pmc⁢2₁ and Amm2 phases. In contrast to the conclusions drawn from SXRD, PDF reveals structures having lower symmetry (with coexisting Cc+ Pmc2₁ phases at 1.7 ≤r≤ 20 Å) at short ranges for these PPBs. In conclusion, the presence of different long- and short-range symmetries (accommodating tilt-oriented ferroelectric phases) in the unique polymorphic phase boundaries makes them thermally stable and advantageous for technological applications.« less

Dielectric loss is known to limit state-of-the-art superconducting qubit lifetimes. Recent experiments imply upper bounds on bulk dielectric loss tangents on the order of 100 parts per billion but because these inferences are drawn from fully fabricated devices with many loss channels, these experiments do not definitely implicate or exonerate the dielectric. To resolve this ambiguity, we devise a measurement method capable of separating and resolving bulk dielectric loss with a sensitivity at the level of 5 ×10^–9. The method, which we call the dielectric dipper, involves the in situ insertion of a dielectric sample into a high-quality microwave cavitymore » mode. Smoothly varying the participation of the sample in the cavity mode enables a differential measurement of the dielectric loss tangent of the sample. The dielectric dipper can probe the low-power behavior of dielectrics at cryogenic temperatures and does so without the need for any lithographic process, enabling controlled comparisons of substrate materials and processing techniques. We demonstrate the method with measurements of sapphire grown by edge-defined film-fed growth (EFG) in comparison to high-grade sapphire grown by the heat-exchanger method (HEMEX). For EFG sapphire, we infer a bulk loss tangent of 63⁢(8) ×10^–9 and a substrate-air interface loss tangent of 15⁢(3) ×10^–4 (assuming a sample surface thickness of 3 nm). For a typical transmon, this bulk loss tangent would limit device quality factors to Q ≲20 ×10⁶, suggesting that bulk loss is likely the dominant loss mechanism in the longest-lived transmons on sapphire. We also demonstrate this method on HEMEX sapphire and bound its bulk loss tangent to be less than 19⁢(6) ×10^–9. As this bound is about 3 times smaller than the bulk loss tangent of EFG sapphire, the use of HEMEX sapphire as a substrate would lift the bulk dielectric coherence limit of a typical transmon qubit to several milliseconds.« less

Strongly correlated ground states and exotic quasiparticle excitations in low-dimensional systems are central research topics in the solid-state research community. The present work develops a layered material and explores the physical properties. Single crystals of 3⁢R–Na₂⁢MnTe⁢O₆ were synthesized via a flux method. Single-crystal x-ray diffraction and transmission electron microscopy reveal a crystal structure with ABC-type stacking and an R–3 space group, which establishes this material as a stacking polytype to previously reported 2⁢H–Na₂⁢MnTe⁢O₆. Magnetic- and heat-capacity measurements demonstrate dominant antiferromagnetic interactions, the absence of long-range magnetic order down to 0.5 K, and field-dependent short-range magnetic correlations. A structural transition atmore » ~23 K observed in dielectric measurements may be related to displacements of the Na positions. In conclusion, our results demonstrate that 3⁢R–Na₂⁢MnTe⁢O₆ displays low-dimensional magnetism, disordered structure and spins, and the system displays a rich structure variety.« less

Aberration corrected scanning transmission electron microscopy (STEM) and electron diffraction have been used to disclose local structure and nano-chemistry in a Ca modified BaTiO₃-Bi(Mg_0.5Ti_0.5)O₃ relax or dielectric ceramic which exhibits high and near-invariant relative permittivity over a wide temperature range. High resolution, synchrotron X-ray diffraction indicated a globally cubic structure ($Pm$$$$\overline{3}$$$$m$), but direct atomic-scale imaging by STEM revealed local tetragonal distortions. Nanopolar clusters were identified from B-site atomic displacement vectors measured relative to oxygen ion positions along < 100 > and < 110 > zone axes of integrated differential phase contrast (iDPC) STEM images, highlighting cluster sizes of 2–5 nm.more » Chemical analysis by STEM-energy dispersive X-ray spectroscopy and full pattern refinements of X-ray powder diffraction data each implied high levels of Bi vacancies within the matrix. The possibility that these A-site vacancies modulate the nanopolar structure and promote flattening of the permittivity-temperature response in this class of dielectric is discussed.« less

Environmentally friendly piezoceramics Bi_1/2(Na_0.78K_0.22)_1/2Ti_1-x(Fe_1/2Nb_1/2)_xO₃ (BNKT-FN) with FeNb (FN) ratios 0, 0.01, 0.02, 0.03 and 0.04 were synthesized via conventional solid-state reaction (CSSR). X-ray diffraction (XRD) analysis revealed that the FN complexes were completely dissolved in BNKT perovskite and the structural transition occurred from ferroelectric to relaxor state. The average grain sizes for x = 0, 0.01, 0.02, 0.03 and 0.04 were found to be 0.34 μm, 0.35 μm, 0.38 μm, 0.32 μm and 0.39 μm, respectively. It is observed that the grain size increased with the addition of FN, except for x = 0.03. Here, the coercive field (E_c) andmore » remnant polarization (P_r) of the system were decreased with increasing FN concentration and the highest E_c of 21.1 kV/cm and P_r of 29.2 μC/cm² were noted for the base pure sample. In addition, the increase of FN content steadily broadened the dielectric anomaly at maximum dielectric constant temperature (T_m) in the BNKT-FN system. Consequently, unipolar normalized strain (S_max/E_max) was found to be enhanced monotonically achieving the highest value of around 654 pm/V (x = 0.02). These properties suggest that the investigated system could be a promising eco-friendly candidate for piezoelectric actuators and many other applications requiring high piezoelectric induced strain.« less

BaZrO₃ is reportedly one of few perovskites that retains an ideal cubic structure down to zero Kelvin even though its ground state as predicted by first-principles calculations has remained contentious. Here, we combine electron diffraction with total neutron scattering measured on ceramic samples at cryogenic temperatures to demonstrate that below 80 K, this compound undergoes a structural change associated with the onset of correlated out-of-phase rotations of [ZrO₆] octahedra. Here, the change is manifested in the appearance of weak but relatively sharp superlattice reflections at ½hkl (h, k, l = odd), which are readily detectable by electron diffraction. Atomistic structuralmore » refinements from the total neutron scattering data confirmed that these reflections are associated with octahedral tilting. The observed rotations are consistent with the a⁰a⁰c^- type and feature a coherence length of about 3 nm. The average structure of BaZrO₃, as seen by Bragg diffraction, remains cubic. According to the electron diffraction data, Nb-doped BaZrO₃ undergoes a similar structural transition but in this case, the tilting couldn't be recovered from the neutron scattering, suggesting that the distortions are smaller compared to those in the pure compound.« less

The growing need for classical as well as quantum optical sensing places increasingly stringent requirements upon the desired characteristics of the engendered fields. Specifically, achieving superior field enhancement plays a critical role in applications ranging from chem-bio sensing, Raman and infrared spectroscopies to ion trapping and qubit control in emerging quantum-information science. Due to their low optical losses and ability to exhibit resonant field enhancements, all dielectric multilayers are emerging as an optical material system not only useful to classical photonics and sensing but also of potential to be integrated with quantum materials and quantum sensing. The recently introduced conceptmore » of zero-admittance layers [1] within dielectric multilayer materials, enables the creation and control of resonant fields orders of magnitude larger than the exciting field. Here, invoking the zero-admittance concept, we design, fabricate, and characterize an all-dielectric nonabsorbing stack and demonstrate the engendered huge field enhancement. Describing the fields in terms of Bloch surface waves, we connect the surface field to the semiperiodicity in the dielectric domains of the stack. As a specific application of the resonant field, we propose and demonstrate refractive-index sensing for the detection of trace amounts of an analyte. The results include a quantification of the sensitivity of the device with respect to the profile of the exciting field. The experimental results are shown to be in good agreement with theoretical calculations.« less

Ferromagnetic gadolinium silicide (Gd₅Si₄) nanoparticles significantly enhance the microwave absorption bandwidth of a polymer blend (PVB-PEDOT:PSS). These materials are essentially needed for various military and civilian applications such as X-band (8.2–12.4 GHz) and Ku-band (12.4–18 GHz) absorption. A single 1.2 mm thick layer of PVB-PEDOT:PSS-Gd₅Si₄ (PPGS) nanocomposite film demonstrates the most promising bandwidth (8.2–18 GHz) with a minimum reflection loss of -14 dB. Mechanistically, dielectric loss ($$\mathcal {tan}$$δ_e ≈2.4) and magnetic loss ($$\mathcal {tan}$$δ_m ≈1.1) contributes more efficiently, and standard microwave simulation confirms the stored energy is predominant in PPGS nanocomposite which enhances the bandwidth.