Ceramics

Multiphasic calcium phosphate (CaP) composites made of hydroxyapatite (HAp), α-tricalcium phosphate (α-TCP), or β-tricalcium phosphate (β-TCP) are promising for biomedical applications. In this paper, the changes in Raman spectra of a series of HAp/α-TCP and HAp/β-TCP were calibrated and new algorithms using microRaman spectroscopy were established for an efficient and quantitative analysis of the constituent phases in multiphasic CaP systems, taking advantages of their characteristic Raman bands. The reliability of the proposed Raman algorithms was further examined and verified by the investigation of a tri-phase CaP mixture and thermally treated monolithic ceramics of HAp, α-TCP and β-TCP using both Raman and XRD analyses. The results demonstrated the applicability of the proposed method for quantitative phase evaluation, as well as higher sensitivity of Raman spectroscopy to nonstoichiometric alteration for more precise phase control and quality evaluation in the presence of defects in multiphasic CaP systems.

Lead-free (1−x)(K_0.49Na_0.51)(Nb_0.95Sb_0.05)O₃-xSr(Fe_0.5Nb_0.5)O₃ [(1−x)KNNbS-xSrFNb, x = 0.01–0.07] ceramics with 0.5 wt% CuO were prepared by conventional sintering (CS) and two-step sintering (TSS). Increasing the SrFNb content drives the structure from orthorhombic–tetragonal (O-T, x ≤ 0.03) coexistence to rhombohedral–tetragonal (R-T, x ≥ 0.05) coexistence, and shifts the phase boundary toward room temperature, while Fe³⁺/Nb⁵⁺ B-site disorder induces polar nanoregions, diffuse dielectric behavior (dispersion index γ > 1.7) and a drop of T_m (temperature of dielectric constant maximum) from 295 °C to below room temperature. Increasing SrFNb significantly reduces the average grain size from 0.6 μm to 0.3 μm, while TSS decouples densification from grain growth, raising the maximum relative density from 92.13% to 94.51% at x = 0.05 with only a slight reduction in average grain size from 0.35 μm to 0.32 μm. These changes directly tailor the electrical properties: the near-room-temperature O-T boundary at x = 0.03 gives the best soft-type response (piezoelectric constant d₃₃ = 133 pC/N, electromechanical coupling coefficient K_p = 0.285, remnant polarization P_r = 22.72 μC/cm²), whereas acceptor-oxygen-vacancy dipoles at x = 0.01 pin domain walls, yielding the highest mechanical quality factor Q_m = 329 with low tan δ, and TSS further improves fatigue resistance. Combining SrFNb-driven structural evolution with TSS microstructural control thus offers an effective route to tailor KNN-based lead-free piezoelectrics.

This work elucidates the growth of lithium nickel cobalt manganese oxide (NCM)/lithium lanthanum zirconate (LLZO)/zinc ferrite (ZFO) films using X-ray diffraction (XRD), Rutherford backscattering (RBS), electron probe microanalysis (EPMA) and X-ray absorption spectroscopy (XAS). Prior to deposition of LLZO and NCM/LLZO, ZFO films (deposition times: 25 (NLZ25) and 100 min (NLZ100)) were deposited on silicon (100) substrates using radio frequency (RF) sputtering at a base pressure of 5.0 × 10⁻⁶ Torr. LLZO was deposited for 90 min at RF power of 40 W. Thereafter, an NCM layer was deposited on these bilayer structures for 100 min (RF power—35 W). Obtained trilayer structures were annealed at 900 °C for 1 h. XRD shows ZFO is able to attain crystalline phase of spinel structure for both NLZ25 and NLZ100. In the trilayer structures onsets of some impurity phases are observed. RBS analysis reveals that for NLZ25, NCM, LLZO, and ZFO layers have thicknesses of approximately 30, 60, and 70 nm. For NLZ100, the corresponding layer thicknesses are 40, 90, and 200 nm, respectively. The significant change in ZFO thickness is attributed to the longer deposition duration for later cases. The O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra of grown trilayer structures exhibit spectral features associated with ZFO, LLZO and NCM. The pre-edge region in the O K-edge NEXAFS spectra is strongly influenced by the interaction of ions from various layers in these structures. La M-edge NEXAFS spectra exhibit characteristic spectral features of La ions in LLZO and show the presence of La³⁺ in respective layers.