Polymorphic Phase Research Articles

High dielectric temperature stability in the relaxor ferroelectric thin films via using a multilayer heterostructure

The temperature stability of the relaxor ferroelectrics (RFEs) mainly originates from the diffuse phase transition (DPT). Higher atomic disorder degrees, more inhomogeneous lattice distortion and polymorphic phases could increase the compositional inhomogeneity for a stronger DPT. This work aims to enhance this compositional inhomogeneity for a high dielectric temperature stability by preparing the multicomponent RFE-based multilayer heterostructure polycrystalline thin films. The as-prepared RFE thin films show a relatively high dielectric constant (∼165.14), and a very high dielectric temperature stability with a very low relative variation ratio of dielectric constant (∼1.7 %) from -55 °C to 150 °C which can be comparable to most linear dielectric thin films. Meanwhile, the dielectric loss and leakage current densities were also optimized. This work brings the potential application of the RFE thin films in the thin-film capacitor with high temperature stability requirements.

Phase Engineering of Two‐Dimensional Transition Metal Dichalcogenides

Since the successful isolation of single‐layer graphene with an atomic thickness, various van der Waals (vdW) materials have been intensively studied owing to their unique properties. Among the families of vdW materials, transition metal dichalcogenides (TMDs) have served as representatives because of their diverse band structures and intriguing quantum states, unlike those observed in their bulk counterparts. Particularly, unconventional polymorphic phases of TMDs increase the degrees of freedom in device fabrication and property modulation. As variations in structural phases significantly change the electrical, physical, and chemical properties of materials, phase engineering is essential for the new paradigm of TMD‐based devices. In this review, diverse strategies that can induce and control structural phases in TMDs are explored. After introducing the polymorphic phase changes and the resulting electronic band structures, the various empirical approaches used for manipulating phases in vdW materials, including phase‐selective synthesis and post‐synthesis treatments, are summarized. The group‐VI TMDs are considered as reference, and the analysis is extended to other TMDs across various groups in the periodic table. In addition to providing a comprehensive survey of the recent progress in TMD applications, the challenges for TMD applications and potential opportunities in emerging fields are discussed.

Characterization of iron oxides: Valence states and naturally occurring polymorphs using chemical shift of X–ray FeLβ1 line by WD–XRF

In X–ray spectroscopic studies of 3d transition metals, Kβ1,3 lines have been extensively used for the examination of chemical states. This is because Kβ1,3 lines are the second most intense X–ray lines and are more sensitive to changes in chemical state of 3d transition metals since the valence shell 3p is involved in the transition. In order to characterize iron oxides in natural iron ores, we determined the chemical shift, asymmetric index and FWHM of the third order FeKβ1,3 lines using WD–XRF technique. Unfortunately, none of these parameters exhibited good agreement with the chemical state of iron which was desired for characterization of iron oxides. Alternatively, FeL-lines were inspected because it involves the valence shell 3d electrons and moreover Fe(II) and Fe(III) have different number of unpaired electrons in the 3d shell. Hence, FeL-lines are anticipated to represent signature of different chemical states of iron. The study established a linear relationship between chemical shift of FeLβ1 line (δβ) and spin multiplicity (2S+ 1) in iron oxide ores having both Fe(II) and Fe(III) valence states. Since (2S + 1) is an intrinsic property of valence state, the study of δβ facilitated speciation of iron. The δβ also contained potential information on structural framework of iron oxides whereby it enabled characterization of various polymorphic phases of iron oxides irrespective of their crystalline/amorphous forms and structure. The δβ was found to increase with increase in Fe(III)/Fetotal ratio in the iron oxide CRMs. Hematite (α–Fe2O3) was observed to have higher δβ than maghemite (γ–Fe2O3) which is attributed to differences in their packing structure. Magnetite (Fe3O4), on the other hand, showed an anomalous behavior due to structural resemblance with maghemite, but both were characterized successfully.

Spherical CaCO3: Synthesis, Characterization, Surface Modification and Efficacy as a Reinforcing Filler in Natural Rubber Composites

Natural rubber (NR), an important natural polymer derived from the Hevea brasiliensis tree, has been widely used in the rubber industry owing to its excellent elastic properties. However, it requires reinforcing fillers to improve its mechanical properties for the manufacturing of rubber products. Generally, calcium carbonate (CaCO3) is employed as a non-reinforcing filler. This work aimed to synthesize spherical-shaped CaCO3 at a submicrometric scale without and with surface treatment and explore its utilization as a reinforcing filler in NR composites. The morphological shape and polymorphic phase of CaCO3 were investigated using SEM, TEM, XRD, ATR-FTIR and Raman techniques. The mechanical properties of various amounts (0 to 60 phr) of CaCO3-filled NR composites were explored. As a result, the NR/treated CaCO3 composites provided higher tensile strength than the NR/untreated CaCO3 composites and pure NR at all filler loadings. This may have been due to the improved interfacial interaction between NR and CaCO3 with the improved hydrophobicity of CaCO3 after treatment with olive soap. The optimal filler loading was 20 phr for the highest tensile strength of the rubber composites. In addition, the elongation at break of the NR/treated CaCO3 was slightly decreased. Evidence from SEM and FTIR revealed the vaterite polymorph and shape stability of CaCO3 particles in the NR matrix. The results demonstrate that the particle size and surface treatment of the filler have essential effects on the mechanical property enhancement of the rubber composites. Synthesized spherical CaCO3 could be a potential reinforcing filler with broader application in polymer composites.

Enhanced electrocaloric effect in KNN-based ceramic via polymorphic phase transition

A large adiabatic temperature change (ΔT) in lead-free ceramics is highly desired to develop eco-friendly and high efficiency solid-state refrigeration device based on electrocaloric effect (ECE). However, a large ΔT is often obtained near high Curie temperature (Tc > 100 °C), which impedes the practical applications for electrocaloric refrigeration technology. Herein, the lead-free (1-x)(K0.48Na0.535)0.03Li0.07(Nb0.99Sb0.01)O3-xBaZrO3 (x = 0, 0.02, 0.04 and 0.06) ceramics were synthesized through a conventional solid-state sintering method. A polymorphic phase transition (PPT) region is constructed by composition engineering to achieve large ECE near the ambient temperature. A ΔT of 0.48 K under 50 kV/cm is obtained at 60 °C by using the direct measurement in KNLNS-0.02BZ ceramic with coexistence of R-O-T phase. This work suggests that building multi-phase coexistence is a feasible design scheme in order to achieve ECE near the room temperature.

Optimizing Output Power Density in Lead-Free Energy-Harvesting Piezoceramics with an Entropy-Increasing Polymorphic Phase Transition Structure.

It is an urgent need to develop lead-free piezoelectric energy harvesters (PEHs) to address the energy dilemma and meet environmental protection requirements. However, the low output power densities limit further promotion of lead-free PEHs for use in daily life. Here, an entropy-increasing strategy is proposed to achieve an increased output power density of 819 μW/cm3 in lead-free potassium sodium niobate (KNN)-based piezoceramics by increasing the configuration entropy and realizing nearly two times the growth compared with low-entropy counterparts. Evolution of the energy-harvesting performance with increasing configuration entropy is demonstrated systematically, and the excellent energy-harvesting properties achieved are attributed to the enhanced lattice distortion, the flexible polarization configuration, and the high-density randomly distributed nanodomains with the entropy-increasing effect. Moreover, excellent vibration fatigue resistance and variable temperature output power characteristics were also realized in the PEH prepared by the proposed entropy-increasing material. The significant enhancement of the comprehensive energy-harvesting performance demonstrates that the construction of KNN-based ceramics with high configuration entropy represents an effective and convenient strategy to enable design of high-performance piezoceramics and thus promotes the development of advanced PEHs.

Stabilization of the VO2(M2) Phase and Change in Lattice Parameters at the Phase Transition Temperature of WXV1-XO2 Thin Films.

Various methods have been used to fabricate vanadium dioxide (VO2) thin films exhibiting polymorph phases and an identical chemical formula suited to different applications. Most fabrication techniques require post-annealing to convert the amorphous VO2 thin film into the VO2 (M1) phase. In this study, we provide a temperature-dependent XRD analysis that confirms the change in lattice parameters responsible for the metal-to-insulator transition as the structure undergoes a monoclinic to the tetragonal phase transition. In our study, we deposited VO2 and W-doped VO2 thin films onto silica substrates using a high repetition rate (10 kHz) fs-PLD deposition without post-annealing. The XRD patterns measured at room temperature revealed stabilization of the monoclinic M2 phase by W6+ doping VO2. We developed an alternative approach to determine the phase transition temperatures using temperature-dependent X-ray diffraction measurements to evaluate the a and b lattice parameters for the monoclinic and rutile phases. The a and b lattice parameters versus temperature revealed phase transition temperature reduction from ∼66 to 38 °C when the W6+ concentration increases. This study provides a novel unorthodox technique to characterize and evaluate the structural phase transitions seen on VO2 thin films.

Crystal Structures and Phase Stability of the Li2S-P2S5 System from First Principles.

The Li2S-P2S5 pseudo-binary system has been a valuable source of promising superionic conductors, with α-Li3PS4, β-Li3PS4, HT-Li7PS6, and Li7P3S11 having excellent room-temperature Li-ion conductivity >0.1 mS/cm. The metastability of these phases at ambient temperature motivates a study to quantify their thermodynamic accessibility. Through calculating the electronic, configurational, and vibrational sources of free energy from first principles, a phase diagram of the crystalline Li2S-P2S5 space is constructed. New ground-state orderings are proposed for α-Li3PS4, HT-Li7PS6, LT-Li7PS6, and Li7P3S11. Well-established phase stability trends from experiments are recovered, such as polymorphic phase transitions in Li7PS6 and Li3PS4, and the instability of Li7P3S11 at high temperature. At ambient temperature, it is predicted that all superionic conductors in this space are indeed metastable but thermodynamically accessible. Vibrational and configurational sources of entropy are shown to be essential toward describing the stability of superionic conductors. New details of the Li sublattices are revealed and are found to be crucial toward accurately predicting configurational entropy. All superionic conductors contain significant configurational entropy, which suggests an inherent correlation between fast Li diffusion and thermodynamic stability arising from the configurational disorder.

Effect of organic acids on the solid-state polymorphic phase transformation of piracetam

Metastable polymorphs are frequently used in oral solid dosage forms to enhance the absorption of poorly water-soluble drug compounds. However, the solid phase transformation from the metastable polymorph to the thermodynamically stable polymorph during manufacturing or storage poses a major challenge for product development and quality control. Here, we report that low-content organic acids can exhibit distinct effects on the solid-state polymorphic phase transformation of piracetam (PCM), a nootropic drug used for memory enhancement. The addition of 1 mol% citric acid (CA) and tricarballylic acid (TA) can significantly inhibit the phase transformation of PCM Form I to Form II, while glutaric acid (GA) and adipic acid (AA) produce a minor effect. A molecular simulation shows that organic acid molecules can adsorb on the crystal surface of PCM Form I, thus slowing the movement of molecules from the metastable form to the stable form. Our study provides deeper insights into the mechanisms of solid-state polymorphic phase transformation of drugs in the presence of additives and facilitates opportunities for controlling the stability of metastable pharmaceuticals.

Domain size control by spinodal decomposition in ferroelectrics

Just as fine precipitate dispersions are sought for high yield strength in alloys, nanoscale, mixed-phase microstructures are sought for high electromechanical performance in oxide ferroelectric materials. Spinodal decomposition is an effective route to fine-scale alloy microstructures and is exploited commercially, for example, in bronzes. Spinodal decomposition has been linked to nanoscale ferroelectric microstructures, but a comprehensive analysis is missing. Here spinodal decomposition in ferroelectric crystals is analysed in 3D including the local electric field using the ferroelectric multi-phase field model for polymorphic phase boundary (PPB) systems. A polarisation consulate temperature Tsp is identified: in single phase ferroelectric, Tsp=Tcw, and, in PPB ferroelectrics, Tcw,ζ=0<Tsp<Tcw,ζ=1. The stability of fluctuations in polarisation depends on temperature, is isotropic in wavevector k→, and corresponds to 2D waves in ceramics. General predictions are summarised and specific predictions for single phase and a PPB system (1−x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) are made. At 284K, the minimum wavelength is lcritBT=166nm in BaTiO3 and lcritPZT=1.70nm in Pb(Zr,Ti)O3, suggesting that spinodal decomposition is less likely to be observed in BaTiO3. For BZT-40BCT, the minimum observable wavelength at TPPB is ∼22 unit cells lcritBZT−40BCT=8.72nm and presents a viable route to nanoscale rhombohedral + tetragonal microstructures. Domain size engineering by spinodal decomposition with controlled grain structures and quenching in oxide and organic ferroelectrics is identified as a new route to optimise performance.

Pressure-Driven Polymorphic Transition, Emergent Insulator-To-Metal Transition, and Photoconductivity Switching in Violet Phosphorus.

Polymorphic phase transition is an essential phenomenon in condensed matter that the physical properties of materials may undergo significant changes due to the structural transformation. Phase transition has thus become an important means and dimension for regulating material properties. Herein, this study demonstrates the pressure-induced multi-transition of both structure and physical properties in violet phosphorus, a novel phosphorus allotrope. Under compression, violet phosphorus undergoes sequential polymorphic phase transitions. Concomitant with the first phase transition, violet phosphorus exhibits emergent insulator-metal transition, superconductivity, and dramatic switching from positive to negative photoconductivity. Remarkably, the resistance of violet phosphorus shows a sudden drop of around 107 along with the phase transition. In addition, piezochromism from translucent red to opaque black and suppression of photoluminescence are observed upon compression. Of particular interest is that the sample irreversibly transforms into black phosphorus with a pronounced discrepancy in physical properties from the pristine violet phosphorus after decompression. The abundant polymorphic transitions and property changes in violet phosphorus have significant implications for designing novel pressure-responsive electronic/optoelectronic devices and exploring concealed polymorphic transition materials.

Investigation into polymorphism within ethenzamide-ethylmalonic acid cocrystal using Raman and terahertz vibrational spectroscopy

Two cocrystal polymorphs of ethenzamide (ETZ) and ethylmalonic acid (EMA) were synthesized by solvent evaporation. Crystal structure analysis revealed that the main amide − carboxyl heterosynthon in ETZ-EMA cocrystal Form I and Form II are the same, but the crystal structure of these two polymorphs are different. Terahertz (THz) and Raman vibrational spectroscopy were used to characterize ETZ, EMA, ETZ-EMA cocrystal polymorph Form I and Form II respectively. The experimental results showed that ETZ, EMA, ETZ-EMA cocrystal Form I and ETZ-EMA cocrystal Form II exhibited completely different characteristic peaks. Both THz and Raman vibrational spectroscopy can be used to distinguish ETZ-EMA cocrystal Form I from Form II. Furthermore, the investigation of phase transition induced by temperature and solid-state grinding was also performed. In the temperature phase transition experiments, when the powder sample was heated to a temperature range of 80–82 °C, the metastable ETZ-EMA cocrystal Form I transformed into the more stable ETZ-EMA cocrystal Form II. Solid-state grinding analysis revealed that the results of the ETZ-EMA cocrystal polymorph synthesis in grinding experiments depended on the polarity of the solvents used. Grinding without solvent or with high polarity solvents tended to result in the stable ETZ-EMA cocrystal Form II. Moreover, the metastable ETZ-EMA cocrystal Form I would transform into Form II after further grinding process. These results demonstrate that THz and Raman vibrational spectroscopy have high sensitivity and accuracy in the detection of both cocrystal synthesis and cocrystal polymorph phase transitions.

Domain reorientation and electric-field-induced phase transition in (K,Na)(Nb,Sb)O3-(Bi,Na)ZrO3 piezoceramics

Polymorphic phase transition boundary (PPB) strategy is effective in designing high-performance piezoelectric materials in (K0.5Na0.5)NbO3 (KNN)-based systems. However, the underlying mechanism of large piezoelectric response in KNN-based is still blurry and thus needs to be explored properly. In this paper, it is found that the domain reorientation becomes easier and more sufficient in the KNN-based ceramics with two-phase coexistence. Moreover, in situ transmission electron microscope experiments disclose the occurrence of a new intermediate phase under an external electric filed, which could relieve the internal stress generated by the domain reorientation and then facilitate the further domain switching along the electric field direction. The enhanced domain reorientation contributes to the high piezoelectric response in PPB region (d33 = 438 pC/N, kp = 48%, d33* = 520 p.m./V at 1.5 kV/mm). Our work provides an in-depth understanding of the contribution of the domain switching and electric-filed-induced phase transition to piezoelectric properties in KNN-based ceramics, which shall benefit the design of new lead-free high-performance piezoelectric materials.

Hexagonal Phase Formation and Crystalline Structural Transition in Long-Spaced Aliphatic Polyesters with Side Groups.

Side substitution is an effective method for the chemical modification and functionalization of linear polyesters. The presence of side groups can have a profound effect on the crystalline structure and phase transition of semicrystalline polyesters. Herein, we synthesized the long-spaced polyesters with -OH and -CH3 side groups and various methylene segment lengths and studied the effects of the side groups on the crystal polymorph and phase transition of substituted polyesters. The substituted polyesters grow in the thermally stable phase (form I) at a higher temperature. However, the polyesters crystallize in a metastable hexagonal phase (form II) with trans chain conformation at a lower temperature. The metastable form II transforms into the more stable form I during long-time annealing or upon heating; this phase transition is accompanied by chain tilting and crystal lamellar thickening. This study has elucidated the critical role of side groups in the polymorphic crystallization and phase transition of linear polyesters.

A novel energetic cocrystal of DATNBI/TNT with low sensitivity and an unexpected polymorphic transition

A novel type of 4,4′,5,5′-tetranitro-1H,1′H-(2,2′-biimidazole)-1,1′-diamine (DATNBI)/TNT energetic cocrystal (cocrystal-1) was prepared by the solvent evaporation method. The molar ratio of the cocrystal is 1:2 and the crystal density is 1.784 g cm−3 at 23°C. It belongs to the triclinic system with space group P 1. The thermal stability, mechanical sensitivity and detonation performance of cocrystal-1 were studied. Compared with DATNBI, the mechanical sensitivity (H 50 and FS, friction sensitivity) and thermal stability (T d, detonation temperature) of cocrystal-1 were significantly improved (H 50, FS and T d of DATNBI and cocrystal-1 are, respectively, 27.8 cm, 160 N, 240°C and 65.6 cm, &gt;360 N, 253°C). Combining these results with other characterizations, it was found that cocrystal-1 exhibited a polymorphic transformation, phase separation and melting of the two single components in succession. The ability to control the properties and understand the structural stability of this explosive cocrystal is of great value.

Defect Dipole‐Induced Fatigue Strain Recoverability in Lead‐Free Piezoelectric Ceramics

AbstractPiezoelectric ceramics have garnered extensive utilization in high‐precision actuators, where the magnitude of electric field‐induced strain and fatigue resistance play crucial roles in actuation applications. Herein, an innovative strategy based on defect dipoles is proposed to form a defect‐engineered polymorphic phase transition and achieve a giant piezoelectric strain coefficient of 3080 pm V−1 in Li/Sr‐doped (K0.5Na0.5)NbO3 lead‐free piezoceramics. The mechanism responsible for the enhanced strain performance lies in the optimized strain compatibility between the refined stripe domains and the nanosized domains. Additionally, the results demonstrate that the material is able to recover from fatigue‐induced strain depletion under the stimulation of bipolar electric fields. This property can be phenomenologically explained by the rigid ion model, in which the application of reversal electric fields can facilitate the restoration of defect dipoles, thereby greatly contributing to strain recoverability. This study establishes a close correlation between the unipolar strain properties and the inherent flexibility of defect dipoles and provides new insight into the design of high‐reliability, large‐stroke piezoceramics.

Developing fired clay bricks by incorporating scrap incinerated waste and river dredged sediment

The global extraction of several billions of clean clay resources, which destroy millions square meters of land, is triggering environmental problems. Incorporating different dosages of incinerated waste or dredged sediment in bricks production has been studied by many researchers. Research articulating the combined effect of incinerated waste material (IWM) and river dredged sediments (RDS) addition on the performance of bricks is scarce. This paper aims to present findings on the engineering performance of fired bricks developed with the addition of IWM and RDS. In this regard, bricks were made with 5 wt% IWM and different dosages of RDS (i.e., 0 – 15 wt%). Physical, durability, mechanical, thermal and microstructure of the developed bricks is examined. Bricks’ shrinkages were found meeting quality performance criterion in the 1.42 – 4.11% range. The highest bulk density of 1.85 g/cm3 permit to classify bricks obtained as lightweight. Water absorptions were mostly within the acceptable 20% tolerance level postulating the developed bricks high durability standard. Compressive strength reductions, which were confined within 5.28 and 21.57 MPa, showed the developed bricks applicability to structural weight-supporting construction as well as specialized engineering construction works. The 40.5% thermal conductivity reduction in WB15 bricks (at 800 °C) theorized its suitability for thermal insulation construction. Mineralogical and morphological analyses of fired bricks clearly showed kaolinite polymorphic phase transformation, which contributed to the different morphologies in the brick matrices. Consequently, reuse of IWM and RDS offered a chance to advance sustainable use of scarce clay resources in lightweight and thermal insulation brick production.

Phase Structures, Electromechanical Responses, and Electrocaloric Effects in K0.5Na0.5NbO3 Epitaxial Film Controlled by Non-Isometric Misfit Strain

Environmentally friendly lead-free K1-xNaxNbO3 (KNN) ceramics possess electromechanical properties comparable to lead-based ferroelectric materials but cannot meet the needs of device miniaturization, and the corresponding thin films lack theoretical and experimental studies. To this end, we developed the nonlinear phenomenological theory for ferroelectric materials to study the effects of non-equiaxed misfit strain on the phase structure, electromechanical properties, and electrical response of K0.5Na0.5NbO3 epitaxial films. We constructed in-plane misfit strain (u1−u2) phase diagrams. The results show that K0.5Na0.5NbO3 epitaxial film under non-equiaxed in-plane strain can exhibit abundant phase structures, including orthorhombic a1c, a2c, and a1a2 phases, tetragonal a1, a2, and c phases, and monoclinic r12 phases. Moreover, in the vicinity of a2c−r12, a1c−c, and a1a2−a2 phase boundaries, K0.5Na0.5NbO3 epitaxial films exhibit excellent dielectric constant ε11, while at a2c−r12 and a1c−c phase boundaries, a significant piezoelectric coefficient d15 is observed. It was also found that high permittivity ε33 and piezoelectric coefficients d33 exist near the a2c−a2, a1a2−r12, and a1c−a1 phase boundaries due to the existence of polymorphic phase boundary (PPB) in the KNN system, which makes it easy to polarize near the phase boundaries, and the polarizability changes suddenly, leading to electromechanical enhancement. In addition, the results show that the K0.5Na0.5NbO3 thin films possess a large electrocaloric response at the phase boundary at the a1a2−r12 and a1c−a1 phase boundaries. The maximum adiabatic temperature change ΔT is about 3.62 K when the electric field change is 30 MV/m at room temperature, which is significantly enhanced compared with equiaxed strain. This study provides theoretical guidance for obtaining K1−xNaxNbO3 epitaxial thin films with excellent properties.

A prediction of the thermodynamic, thermophysical, and mechanical properties of CrTaO4 from first principles

AbstractIt is reported that the self‐forming CrTaO4 oxide scale can protect refractory high‐entropy alloys from oxidation, superior to Cr2O3. In this paper, the phase stability, mechanical, and thermal properties of three polymorphous phases of CrTaO4 are systematically investigated from first‐principles density functional theory calculations. The mechanical properties predicted using the strain–energy methods indicated that all three phases are mechanically stable. The temperature dependence of elastic constants and polycrystalline moduli of three phases demonstrated the thermal softening as temperature increase. The Helmholtz‐free energies as a function of volume and temperature are derived from phonon dispersions within the quasi‐harmonic approximation at six strained volumes. The calculated apparent bulk coefficients of thermal expansion of these three phases are evaluated, the highest value approximately 13.4× 10−6 K−1 within a temperature range of 500–2000 K for the rutile I41md phase. The lattice thermal conductivity calculated by the Debye–Callaway model suggested that the rutile type I41md phase has the lowest value of approximately 2.1 W/m/K at 1800 K. The other two phases, C2/m and P2/c, exhibit higher values due to relatively lower Grüneisen parameters and larger phonon velocities. The melting point of CrTaO4 is predicted to be between 1975 and 2449 K using ab initio molecular dynamics simulations. This work provides a comprehensive theoretical understanding of the thermodynamic, mechanical, and thermal properties for the new material CrTaO4 and serves as an example of a viable computational design strategy for improved oxidation resistance of refractory alloys at high temperatures.

Influence of Mn-doping on the structure, high-temperature dielectric, and conductive properties of NaNbO3 ceramics

Single phase NaNb1−xMnxO3 (NMn) with x = 0.00−0.06 ceramics were synthesized using solid state reaction technique at 1150 °C sintering temperature. The Rietveld refinement of XRD patterns of NMn ceramics confirms the orthorhombic phase symmetry with Pbma space group. The field emission scanning electron microscopy (FE-SEM) reveals that grains become denser and larger with doping. The dielectric constant (ϵ′) and tangent loss (tan δ) study has been done at room temperature to 500 °C over a wide frequency in both cooling and heating mode. The anomaly at high temperature region in temperature dependent dielectric constant (ϵ′) plot in both thermal cycle attributes to the P(AFE)-R(AFE) polymorphic phase transition. The relaxor nature of the studied samples strongly depends on dopant concentration and applied field. The impedance analysis reveals negative temperature coefficient of resistance (NTCR) behaviour of material. The Nyquist study suggests the non-Debye characteristic of the dielectric relaxation in NMn ceramics.