Boosting ultra-wide temperature dielectric stability of multilayer ceramic capacitor through tailoring the combination types of polar nanoregions

With the rapid development of space exploration and new energy vehicles,it is urgent to build ultra-wide temperature multilayer ceramic capacitors(UWT MLCCs)to match electronic circuits that can withstand harsh environmental conditions.Relaxor ferroelectrics with diffuse phase transition feature are potential dielectrics for the construction of UWT MLCCs.However,how to ensure high dielectric constant together with low dielectric loss in the wide temperature region is still a big challenge.Here,the above difficulties are addressed by tailoring the combination types of polar nanoregions(PNRs)in the(1-x)(0.8Na_(0.5)Bi_(0.5)TiO_(3)-0.2K_(0.5)Bi_(0.5)TiO_(3))-xNaTaO3(NBT-KBT-xNT)system.Compared with PNRS types of P4bm+R3c and P4bm+Pbnm,the combination type of P4bm+Pbnm+R3c PNRs in NBT-KBT-0.31NT is the most beneficial to obtain comprehensive excellent dielectric performance because it can balance the relationship between high dielectric constant and temperature stability over a wide temperature region.Further,by optimizing the laminating pressure and co-firing temperature to realize a tight interfacial structure between the dielectric layer and the Pt inner electrode,a record-high dielectric constant(er=(907%±15%))together with low dielectric loss(tan δ≤0.025)is achieved over an ultra-wide range from-61℃ to 306℃ for NBT-KBT-0.31 NT MLCC,demonstrating that tailoring the combination types of PNRs is a powerful strategy in designing UWT MLCC dielectrics.

DO WE NEED THE ETHER OF POLAR NANOREGIONS?

This paper deals with possible experimental signatures of the so-called polar nanoregions in lead-based perovskite relaxors.It outlines both traditional and alternative approaches to these signatures.It is argued that the concept of polar nanoregions is useful but largely speculative.Polar nanoregions are compared with ferroelectric nanodomains.Qualitative explanation of the principal"relaxor"properties of PMN are discussed in both frameworks.It is argued that polarization as a vector may not be well defined at any nanometric region in PMN Crystal.

Relaxor behaviour and phase transition of perovskite ferroelectrics-type complex oxides(1–x)Na_(0.5)Bi_(0.5)TiO_3–xCaTiO_3 system

Polycrystalline powders of (1–x)Na_(0.5)Bi_(0.5)TiO_3–xCaTiO_3 ((1–x)NBT–xCT, 0 ≤ x ≤ 0.55) have been synthesized by solid state route. The effects of simultaneous substitution of Na^+/Bi^(3+) at A-site in NBT on structural and dielectric properties were investigated. X-ray diffraction analysis revealed the phase transition from rhombohedral structure(x = 0) to orthorhombic structure(x ≥0.15). A distinct behaviour in dielectric properties was obtained, where for x = 0, a normal ferroelectric behaviour was observed, whereas for x ≥ 0.15, a broad dielectric anomaly was revealed such that the maximum temperature(T_m) strongly depended on the frequency and shifted towards low temperature with CT. The dielectric dispersion indicated a relaxor behaviour revealed by the degree of diffuseness and modelled via Vogel–Fulcher relation. The study highlighted the relaxor behaviour as a function of frequency and proved the transformation from a relaxor high-frequency dependence to a paraelectric phase at temperature T_s. The distinct variation of the Raman spectra at room temperature was correlated with X-ray diffraction results and proved the already mentioned transition. On heating(-193–500 ℃), the Raman spectra confirmed the structural stability(Pnma) of the materials. The phonon behaviour for x = 0.15 was discussed in terms of the appearance of polar nanoregions(PNRs) into a non-polar orthorhombic matrix responsible of the relaxor behaviour. For x = 0.20, unchanged phonon behaviour confirmed the variation in dielectric behaviour where the solids transformed from a relaxor to a paraelectric state without structural phase transition.

RANDOM FIELDS IN RELAXOR FERROELECTRICS—A JUBILEE REVIEW

Substitutional charge disorder as in PbMg_(1/3)Nb_(2/3)O_(3),structural cation vacancies as in Sr_(x)Ba_(1-x)Nb_(2)O_(6) and isovalent substitution of off-centered cations as in BaTi_(1-x)Sn^(x)O_(3) and BaTi1-xZrxO_(3) give rise to quenched electric random-fields(RFs),which we proposed to be at the origin of the peculiar behavior of relaxor ferroelectrics 20 years ago.These are,e.g.a strong frequency dispersion of the dielectric response and an apparent lack of macroscopic symmetry breaking in the low temperature phase.Both are related to mesoscopic RF-driven phase transitions,which give rise to irregularly shaped quasi-stable polar nanoregions below the characteristic temperature T^(*),but above the global transition temperature Tc.Their co-existence with the paraelectric parent phase can be modeled by time-dependentfield equations under the control of quenched RFs and stress-free strain(in the case of order parameter dimension n2).Transitions into global polar order at Tc may occur in uniaxial relaxors as observed on the uniaxial relaxor ferroelectric Sr0.8Ba_(0.2)Nb_(2)O_(6) and come close to RF Ising model criticality.Re-entrant relaxor transitions as observed in solid solutions of Ba_(2)Pr_(0.6)Nd_(0.4)(FeNb_(4))O_(15) are proposed to evidence the coexistence of distinct normal and relaxor ferroelectric phases within the framework of percolation theory.Keywords.

POLAR NANOREGION IN RELAXOR FERROELECTRICS STUDIED BY ANALYTICAL ELECTRON MICROSCOPY

Relaxor ferroelectrics have different properties from that of the normal ferroelectrics,such as dielectric properties with diffuse phase transition and frequency dispersion,specific heat,birefringence,elastic constants and Raman scattering,etc.It is considered that the different properties are related with the polar nanoregions in relaxors.In this work we briefly introduce how we use the high spatial resolution analytical electron microscopy and high resolution electron microscopy methods to investigate the polar nanoregion in Pb(Mg_(1/3)Nb_(2/3))O_(3)(PMN),Pb(Mg_(1/3)Nb_(2/3))O_(3)
PbTiO_(3)(PMN
PT)and Ba(Ti_(1-x)Sn_(x))O_(3)(BTSn).The main experimental results1
10 are as mentioned in next three parts.