Enhancement of pyroelectric properties of lead-free 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics by La doping

Lead-free 0.94NBT-0.06BT-xLa ceramics at x = 0.0–1.0 (%) were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. With increasing La³⁺ content pyroelectric coefficient (p) and figures of merits greatly increase; however, the depolarization temperature (T_d) decreases. p is 7.24 × 10⁻⁴C m⁻² °C⁻¹ at RT at x = 0.5% and 105.4 × 10⁻⁴C.m^−2 °C⁻¹ at T_d at x = 0.2%. F_i and F_v show improvements at RT from 1.12 (x = 0%) to 2.65 (x10 ⁻¹⁰ m v⁻¹) (x = 0.5%) and from 0.021 to 0.048 (m².C⁻¹) respectively. F_i and F_v show a huge increase to 37.6 × 10⁻¹⁰ m v⁻¹ and 0.56 m² C⁻¹ respectively at T_d at x = 0.2%. F_C shows values of 2.10, 2.89, and 2.98 (x10⁻⁹C cm⁻² °C⁻¹) at RT at 33, 100 and 1000 (Hz) respectively. Giant pyroelectric properties make NBT-0.06BT-xLa at x = 0.2% and 0.5% promising materials for many pyroelectric applications.     

Effect of Nd-doping on structural,thermal and electrochemical properties of LaFe0.5Cr0.5O3 perovskites

The structural, thermal and electrochemical properties of the perovskite-type compound La_1−xNd_xFe_0.5Cr_0.5O₃ (x=0.10, 0.15, 0.20) are investigated by X-ray diffraction, thermal expansion, thermal diffusion, thermal conductivity and impedance spectroscopy measurements. Rietveld refinement shows that the compounds crystallize with orthorhombic symmetry in the space group Pbnm. The average thermal expansion coefficient decreases as the content of Nd increases. The average coefficient of thermal expansion in the temperature range of 30–850 °C is 10.12×10⁻⁶, 9.48×10⁻⁶ and 7.51×10⁻⁶ °C⁻¹ for samples with x=0.1, 0.15 and 0.2, respectively. Thermogravimetric analyses show small weight gain at high temperatures which correspond to filling up of oxygen vacancies as well as the valence change of the transition metals. The electrical conductivity measured by four-probe method shows that the conductivity increases with the content of Nd; the electrical conductivity at 520 °C is about 4.71×10⁻³, 6.59×10⁻³ and 9.62×10⁻³ S cm⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. The thermal diffusivity of the samples decreases monotonically as temperature increases. At 600 °C, the thermal diffusivity is 0.00425, 0.00455 and 0.00485 cm² s⁻¹ for samples with x=0.10, 0.15 and 0.20, respectively. Impedance measurements in symmetrical cell arrangement in air reveal that the polarization resistance decreases from 55 Ω cm⁻² to 22.5 Ω cm⁻² for increasing temperature from 800 °C to 900 °C, respectively.     

Oxygen ionic transport in SrFe1−yAlyO3−δ and Sr1−xCaxFe0.5Al0.5O3−δ ceramics

The oxygen permeability of mixed-conducting Sr_1−xCa_xFe_1−yAl_yO_3−δ (x=0–1.0; y=0.3–0.5) ceramics at 850–1000 °C, with an apparent activation energy of 120–206 kJ/mol, is mainly limited by the bulk ionic conduction. When the membrane thickness is 1.0 mm, the oxygen permeation fluxes under pO₂ gradient of 0.21/0.021 atm vary from 3.7×10⁻¹⁰ mol s⁻¹ cm⁻² to 1.5×10⁻⁷ mol s⁻¹ cm⁻² at 950 °C. The maximum solubility of Al³⁺ cations in the perovskite lattice of SrFe_1−yAl_yO_3−δ is approximately 40%, whilst the brownmillerite-type solid solution formation range in Sr_1−xCa_xFe_0.5Al_0.5O_3−δ system corresponds to x>0.75. The oxygen ionic conductivity of SrFeO₃-based perovskites decreases moderately on Al doping, but is 100–300 times higher than that of brownmillerites derived from CaFe_0.5Al_0.5O_2.5+δ. Temperature-activated character and relatively low values of hole mobility in SrFe_0.7Al_0.3O_3−δ, estimated from the total conductivity and Seebeck coefficient data, suggest a small-polaron mechanism of p-type electronic conduction under oxidising conditions. Reducing oxygen partial pressure results in increasing ionic conductivity and in the transition from dominant p- to n-type electronic transport, followed by decomposition. The low-pO₂ stability limits of Sr_1−xCa_xFe_1−yAl_yO_3−δ seem essentially independent of composition, varying between that of LaFeO_3−δ and the Fe/Fe_1−γO boundary. Thermal expansion coefficients of Sr_1−xCa_xFe_1−yAl_yO_3−δ ceramics in air are 9×10⁻⁶ K⁻¹ to 16×10⁻⁶ K⁻¹ at 100–650 °C and 12×10⁻⁶ K⁻¹ to 24×10⁻⁶ K⁻¹ at 650–950 °C. Doping of SrFe_1−yAl_yO_3−δ with aluminum decreases thermal expansion due to decreasing oxygen nonstoichiometry variations.     

The phase stability and thermophysical properties of InFeO3(ZnO)m (m = 2, 3, 4, 5)

The phase stability and thermophysical properties of InFeO₃(ZnO)_m (m = 2, 3, 4, 5) compounds were investigated, which are a general family of homologous layered compounds with general formula InFeO₃(ZnO)_m (m = 1–19). InFeO₃(ZnO)_m (m = 2, 3, 4, 5) ceramics were synthesized using cold pressing followed by solid-state sintering. They revealed an excellent thermal stability after annealing at 1450 °C for 48 h. No phase transformation occurred during heating to 1400 °C. InFeO₃(ZnO)₃ exhibited a thermal conductivity of 1.38 W m⁻¹ K⁻¹ at 1000 °C, which is about 30% lower than that of 8 wt.% yttria stabilized zirconia (8YSZ) thermal barrier coatings. The thermal expansion coefficients (TECs) of InFeO₃(ZnO)m bulk ceramics were in a range of (10.97 ± 0.33) × 10⁻⁶ K⁻¹ to (11.46 ± 0.35) × 10⁻⁶ K⁻¹ at 900 °C, which are comparable to those of 8YSZ ceramics.     

High temperature dielectrics in the ceramic system K0.5Bi0.5TiO3-Ba(Zr0.2Ti0.8)O3-Bi(Zn2/3Nb1/3)O3

Ceramics in the system (1-x)[0.5K_0.5Bi_0.5TiO₃-0.5Ba(Zr_0.2Ti_0.8)O₃]-xBi(Zn_2/3Nb_1/3)O₃ have been fabricated by a solid-state processing route for compositions x≤0.3. The materials are relaxor dielectrics. The temperature of maximum relative permittivity, T_m, decreased from 150 °C for composition x=0, to 70 °C for x=0.2. The x=0.2 sample displayed a wide temperature range of stable relative permittivity, ε_r, such that ε_r=805±15% from −20 to 600 °C (1 kHz). Dielectric loss tangent was ≤0.02 from 50 °C to 450 °C (1 kHz), but due to the tanδ dispersion peak, the value increased to 0.09 as temperatures fell from 50 °C to −20 °C. Values of dc resistivity were of the order of ~10⁹ Ω m at 300 °C. These properties are promising in the context of developing new high temperature capacitor materials.     

Growth and electrical properties of Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 lead-free single crystals by the TSSG method

A series of NBT-KBT lead-free crystals with dimensions of Φ 35×10 mm were successfully grown by the TSSG method. The as-grown crystals possess rhombohedral perovskite structure at room temperature. The curves ε(T) for all crystals show two abnormal dielectric peaks. The depolarization temperatures T_d derived from the first peak of curves tan δ(T) vary with the KBT content, which are 130, 150, 140, and 115 °C respectively, for (100−x)NBT−xKBT (x=5, 8, 12, 15) crystals, being well consistent with the T_d obtained from the temperature dependence of k_t. A notable thermal hysteresis, ΔT≈35 °C, for ferroelectric-antiferroelectric phase transition was also disclosed for 92NBT-8KBT crystal. The investigation of orientation dependence for electrical properties disclosed the dielectric parameters show weak anisotropy. The piezoelectric constants (d₃₃) are 147, 175, 205, 238 pC/N and the values of k_t are 38%, 52%, 52%, 54%, respectively for (100−x)NBT−xKBT (x=5, 8, 12, 15) crystals.     

High-energy storage performance in lead-free (1-x)BaTiO3-xBi(Zn0.5Ti0.5)O3 relaxor ceramics for temperature stability applications

In this paper, we prepared lead-free (1-x)BaTiO₃-xBi(Zn_0.5Ti_0.5)O₃ (x=0.04, 0.08, 0.10, and 0.14) ceramics by a conventional solid-state reaction technique. Pure perovskite structures and dense microstructures were demonstrated for all the compositions. Interestingly, it was found that the sintering temperature tended to decrease with increasing the Bi(Zn_0.5Ti_0.5)O₃ content. It should be stressed that a low sintering temperature of 1050 °C was utilized for the composition of x=0.14. Moreover, the dielectric permittivity-temperature curve became more flat and the relaxor degree became stronger with the augment in Bi(Zn_0.5Ti_0.5)O₃ content. We also conducted a detailed study on the energy storage performance for all the compositions from 25 °C to 180 °C.We found that relatively temperature-stable energy storage performance could be obtained in the compositions with x=0.08, 0.10 and 0.14 regardless of the evolution of dielectric constant during the test temperature range. In particular, due to a higher field of 12 MV m⁻¹, the discharge energy storage densities of x=0.14 could reach 0.81 J cm⁻³, 0.80 J cm⁻³, 0.78 J cm⁻³, 0.72 J cm⁻³, and 0.67 J cm⁻³ with high efficiencies of 94%, 92%, 94%, 88% and 77% at 25 °C, 50 °C, 100 °C, 150 °C, and 180 °C, respectively. All these results demonstrate the (1-x)BaTiO₃-xBi(Zn_0.5Ti_0.5)O₃ ceramics are quite promising for temperature-stable energy storage applications.     

The effect of annealing on electrical properties of fluorinated amorphous carbon films

Fluorinated amorphous carbon (a–C:F) films have been deposited by electron cyclotron resonance chemical vapor deposition (ECR–CVD) at room temperature using C₄F₈ and CH₄ as precursor gases. The chemical compositions and electrical properties of a–C:F films have been studied by X-ray photoelectron spectroscopy (XPS), capacitance–voltage (C–V) and current-voltage (I–V) measurements. The results show that C–CF_x and C–C species of a–C:F films increase and fluorine content decreases after annealing. The dielectric constant of the annealed a–C:F films increases as a result of enhancement of film density and reduction of electronic polarization. The densities of fixed charges and interface states decrease from 1.6 × 10¹⁰ cm^− 2 and (5–9) × 10¹¹ eV^− 1 cm^− 2 to 3.2 × 10⁹ cm^− 2 and (4–6) × 10¹¹ eV^− 1 cm^− 2 respectively when a–C:F films are annealed at 300 °C. The magnitude of C–V hysteresis decreases due to reduced dangling bonds at the a–C:F/Si interfaces after heat treatment. The conduction of a–C:F films shows ohmic behavior at lower electric fields and is explained by Poole–Frankel (PF) mechanism at higher electric fields. The PF current increases indicative of reduced trap energy when a–C:F films are subjected to higher annealing temperatures.     

Nitrate–citrate combustion synthesis of Ce1−xGdxO2−x/2 powder and its characterization

The structure, thermal expansion coefficients, and electric conductivity of Ce_1−xGd_xO_2−x/2 (x = 0–0.6) solid solution, prepared by the gel-combustion method, were investigated. The uniform small particle size of the gel-combustion prepared materials allows sintering into highly dense ceramic pellets at 1300 °C, a significantly lower temperature compared to that of 1600–1650 °C required for ceria solid electrolytes prepared by traditional solid state techniques. XRD showed that single-phase solid solutions formed in all the investigated range. The maximum conductivity, σ_600 °C = 5.26 × 10⁻³ S/cm, was found at x = 0.2. The thermal expansion coefficient, determined from high-temperature X-ray data, was 8.125 × 10⁻⁶ K⁻¹ at x = 0.2.     

Thermal,mechanical and electrical properties of hard B4C,BCN, ZrBC and ZrBCN ceramics

We study the thermal, mechanical and electrical properties of B₄C, BCN, ZrBC and ZrBCN ceramics prepared in the form of thin films by magnetron sputtering. We focus on the effect of Zr_x(B₄C)_1−x sputter target composition, the N₂+Ar discharge gas mixture composition, the deposition temperature and the annealing temperature after the deposition. The thermal properties of interest include thermal conductivity (observed in the range 1.3–7.3 W m⁻¹ K⁻¹), heat capacity (0.37–1.6×10³ J kg⁻¹ K⁻¹ or 1.9–4.1×10⁶ Jm⁻³ K⁻¹), thermal effusivity (1.6–4.5×10³ J m⁻² s^−1/2 K⁻¹) and thermal diffusivity (0.38–2.6×10⁻⁶ m² s⁻¹). We discuss the relationships between materials composition, preparation conditions, structure, thermal properties, temperature dependence of the thermal properties and other (mechanical and electrical) properties. We find that the materials structure (amorphous×crystalline hexagonal ZrB₂-like×nanocrystalline cubic ZrN-like), more than the composition, is the crucial factor determining the thermal conductivity and other properties. The results are particularly important for the design of future ceramic materials combining tailored thermal properties, mechanical properties, electrical conductivity and oxidation resistance.     

Temperature-insensitive dielectric and piezoelectric properties in (1-x)K0.5Na0.5Nb0.997Cu0.0075O3-xSrZrO3 ceramics

Systematic investigation on phase transition, dielectric and piezoelectric properties of (1-x)K_0.5Na_0.5Nb_0.997Cu_0.0075O₃-xSrZrO₃ (x = 0, 0.03, 0.06, 0.09, 0.12, 0.15, abbreviated as KNNC-100xSZ) ceramics was carried out. Due to the coexistence of orthorhombic and tetragonal phase in a wide temperature range, a diffused polymorphic phase transition (PPT) region was achieved in KNNC with x ≥ 0.06. KNNC-12SZ ceramics exhibited high dielectric permittivity (∼1679), low dielectric loss (∼0.02) and small variation (Δe'/ε'_25 °C ≤ 15%) in dielectric permittivity from −78 °C to 237.3 °C. KNNC-6SZ ceramic possessed a high level of unipolar strain (∼0.15%) and maintained a smaller variation of ±12% under the corresponding electric field of 60 kV cm⁻¹ at 10 Hz from 25 °C to 175 °C. d₃₃^*, which was calculated according to the unipolar strain at 60 kV cm⁻¹, was 230 pm V⁻¹ and remained stable below 100 °C. Therefore, our work provided a new promising candidate for temperature-insensitive capacitors and piezoelectric actuators.     

Hidden value in low-cost inorganic pigments as potentially valuable magnetic materials

Inorganic pigments are substances that develop colour in organic solids such as ceramics and glazes, and are usually a complex mixture of oxides, and relatively low-cost. Their chromatic properties have been extensively studied, yet surprisingly the magnetic and electrical properties of these economic and common materials have been neglected, despite the fact many are based on ferrite spinels. Therefore, we investigated these properties in commercial black and brown pigments, to assess their potential as magnetic materials. The brown and black pigments were found to be spinel ferrites, with estimated formulas of Fe_1.34Cr_0.62Mn_0.66Zn_0.22Ni_0.10Co_0.06O₄ and Fe_1.02Cr_0.97Co_0.57Mn_0.23Ni_0.21O₄, respectively. The brown pigment also contained a higher amount of SiO₂ compared to the black pigment (~7 mol% vs. ~2 mol%), which appeared as a second phase of crystalline quartz, and adversely affected its porosity, magnetisation and electrical ac conductivity, compared to the black pigment. However, both were very magnetic and very soft ferrites. The brown pigment had M_s=11.7 A m² kg⁻¹ and H_c of 1.5 kA m⁻¹, with a high electrical conductivity (σ) of 4×10⁻⁴−7×10⁻³ Ω⁻¹ m⁻¹ between 100 Hz and 1 MHz. The black pigment was equally magnetically soft, but had a much greater magnetisation and lower electrical conductivity, with M_s=18.7 A m² kg⁻¹, H_c=2.4 kA m⁻¹, and σ=5×10⁻⁶−8×10⁻⁵ Ω⁻¹ m⁻¹ between 100 Hz and 1 MHz.This work has revealed the potential hidden value of low-cost commercial inorganic pigments based on spinel ferrites as magnetic materials. This demonstrates their potential at low-cost alternative materials for applications such as in power supply transformers, switching materials and sensors, where soft magnetisation is especially important.     

Effects of La doping on electrical conductivity,thermal expansion and electrochemical performance in LaxSr1–xCo0.9Sb0.1O3–δ cathodes for IT–SOFCs

Perovskite oxides La_xSr_1–xCo_0.9Sb_0.1O_3–δ (LSCSbx, x=0.0–0.8) are investigated as IT–SOFC cathodes supported with La_0.9Sr_0.1Ga_0.8Mg_0.2O_3–δ (LSGM) electrolyte. All LSCSbx oxides have a tetragonal distorted perovskite structure with s.g. P4/mmm, while a La₂Co₂O₅ impurity phase was observed within La doping levels at x=0.6–0.8. The LSCSb0.4 has a good chemical compatibility with LSGM electrolyte for temperatures up to 1050 °C. XPS examinations indicate the existence of Co³⁺/Co⁴⁺ mixed valence states in LSCSbx. The conductivity increases with La doping and the LSCSbx with x=0.4 exhibits the highest electrical conductivity (e.g., 673–1637 S cm⁻¹ at 300–850 °C). The thermal expansion coefficient (TEC) decreases from 25.89×10^–6 K^–1 for x=0.0 to 18.5×10^–6 K^–1 for x=0.6 at 30–900 °C. Among the LSCSbx compositions, the LSCSb0.2 exhibits the lowest polarization resistance (R_p), which is merely 0.069 Ω cm² at 700 °C. The maximum power density of the cell with LSCSb0.2 cathode on 300 µm thick LSGM electrolyte attains 564 mW cm^–2 at 850 °C, which is higher than that of SrCo_0.9Sb_0.1O_3–δ (SCSb) cathode. All of the results indicate that LSCSb0.2 is a promising material for application in IT–SOFCs cathodes.     

Study of kinetics in the biosorption of lead onto native and chemically treated olive stone

In this research, olive stone was used as precursor for the development of new biosorbents for lead ions. Chemical treatments were analyzed in terms of their effects on physical–chemical properties and kinetics of lead removal. A kinetic study of the biosorption of lead ions by olive stone was analyzed according to six different kinetic models (pseudo first, pseudo second, pseudo n-order, Elovich, solid diffusion and double exponential models). The biosorption kinetic data were successfully described with pseudo-nth order and double exponential models for all biosorbents. The double exponential model allowed estimating the values of external and internal mass transfer coefficients. The values of external mass transfer coefficient (k_e) ranged from 42.62 × 10⁻⁶ to 508.3 × 10⁻⁶ m min⁻¹ and the internal mass transfer coefficient (k_i) from 3.76 × 10⁻⁶ to 73.4 × 10⁻⁶ m min⁻¹. On the other hand, the analysis of experimental data showed that chemical treatments of the biomass led to increase biosorption capacity of the native biomass.     

Investigations of BaFe0.5Nb0.5O3 nano powders prepared by a low temperature aqueous synthesis and resulting ceramics

A facile method to prepare nanoscaled BaFe_0.5Nb_0.5O₃ via synthesis in boiling NaOH solution is described herein. The nano-crystalline powder has a high specific surface area of 55 m² g⁻¹ and a crystallite size of 15 nm. The as-prepared powder does not show any significant crystallite growth up to 700 °C. The activation energy of the crystallite growth process was calculated as 590 kJ mol⁻¹. Dense ceramics can be obtained either after sintering at 1200 °C for 1 h or after two-step sintering at 1000 °C for 10 h. The average grain sizes of ceramic bodies can be tuned between 0.23 μm and 12 μm. The thermal expansion coefficient was determined as 11.4(3)·10⁻⁶ K⁻¹. The optical band gap varies between 2.90(5) and 2.63(3) eV. Magnetic measurements gave a Néel temperature of 20 K. Depending on the sintering regime, the ceramic samples reach permittivity values between 2800 and 137,000 at RT and 1 kHz.     

Effect of sintering temperature on the structural,electrical and electrochemical properties of novel Mg0.5Si2 (PO4)3 ceramic electrolytes

The objective of the present study is to investigate the effect of sintering temperature on the structural, electrical and electrochemical properties of novel Mg_0.5Si₂ (PO₄) ₃ NASICON structured compound prepared via sol gel method. X-ray diffraction was used to study the structural properties such as crystalline phase and lattice parameters of the solid electrolytes. Electrical properties of the compound were measured using impedance spectroscopy while the electrochemical stability was investigated by linear sweep voltammetry. All the sintering temperatures yielded compounds consisted of monoclinic crystalline phase with a space group of P1 2₁/c1. Lattice parameters for Mg_0.5Si₂ (PO₄) ₃ samples increased from the sintering temperature at 700–800 °C but decreased for sintering temperature at 900 °C. The sample sintered at 800 °C showed the highest total conductivity of 1.83×10⁻⁵ S cm⁻¹ and the highest value of ions mobility, µ of 6.17×10¹⁰ cm² V⁻¹ s⁻¹ which was attributed to the optimum size of migration channel indicated by its unit cell volume. Linear sweep voltammetry result showed that the Mg_0.5Si₂ (PO₄)₃ powder was electrochemically stable up to 3.21 V.     

Microstructural dependence of the thermal and mechanical properties of monazite LnPO4 (Ln = La to Gd)

In this work are given some thermal and mechanical properties of monazite, related to the microstructure. This compound is a poor thermal conductive (λ < 5 W m⁻¹ K⁻¹), with a thermal expansion in between 9 and 10 × 10⁻⁶ K⁻¹ according to the considered crystallographic direction, and a relatively high specific heat (C_p ≈ 110 J mol⁻¹ K⁻¹). Mechanical properties of monazite are characteristic of a brittle behavior: bending strength is of about 100 MPa and fracture toughness is close to 1 MPa m^1/2. Porosity plays a large role on both thermal and mechanical properties pointing out the importance of controlling the whole elaboration process.     

Effect of substrate temperature on structural and electrical properties of BaZr0.2Ti0.8O3 lead-free thin films by pulsed laser deposition

Barium zirconate titanate (BaZr_0.2Ti_0.8O₃, BZT) 250 nm thick thin films were fabricated by pulsed laser deposition and the influence of the substrate temperature on their preferred orientation, microstructure, morphology and dielectric properties was investigated. Dielectric measurements indicated the (1 1 0)-oriented BZT thin films deposited at 750 °C to show good dielectric properties with high dielectric constant (~500 at 100 kHz), low loss tangent (<0.01 at 100 kHz), and superior tunability (>70% at 400 kV/cm), while the largest figure of merit was 78.8. The possible microstructural background responsible for the high dielectric constant and tenability is discussed. In addition, thin films deposited at 750 °C with device quality factor of 8738 and dielectric nonlinearity coefficient of 1.66×10⁻¹⁰ J/C⁴m⁵ were demonstrated.     

Dielectric and thermal properties of AlN ceramics

The effects of slow-cooling and annealing conditions on dielectric loss, thermal conductivity and microstructure of AlN ceramics were investigated. Y₂O₃ from 0.5 to 1.25 mol% at 0.25% increments was added as a sintering additive to AlN powder and pressureless sintering was carried out at 1900 °C for 2 h in a nitrogen flowing atmosphere. To improve the properties, AlN samples were slow-cooled at a rate of 1 °C min⁻¹ from 1900 to 1750 °C, subsequently cooled to 970 °C at a rate of 10 °C min⁻¹ and then annealed at the same temperature for 4 h. AlN and YAG (5Al₂O₃/3Y₂O₃) were the only identified phases from XRD. AlN doped with 0.5 and 0.75 mol% Y₂O₃ had a low loss of <2.0 × 10⁻³ and a high thermal conductivity of >160 W m⁻¹ °C⁻¹.     

Fine structural analysis and phase transition behavior for Li-modified Na0.5K0.5NbO3 lead-free piezoelectric ceramics

The fine crystal structure of Li_x(Na_0.5K_0.5)_1?xNbO₃ ceramics has been studied by means of Nb-K edge extended X-ray absorption fine structure (EXAFS) and X-ray internal strain measurement technique in the vicinity of the compositions showing a polymorphic phase boundary (PPB) between orthorhombic and tetragonal structures. The anisotropic distortion of the NbO₆ octahedral initially occurred when x was increased from 0.050 to 0.053, prior to the completion of the phase transition from orthorhombic to tetragonal symmetry. EXAFS clearly revealed that the bond distance of Nb–O1 with [0 0 1] configuration was increased, and that of Nb–O2 with [1 1 0] configuration was oppositely decreased in the NbO₆ octahedral. In the vicinity of the PPB compositions, the internal strain η_(0 1 1) also increased from 4.5 × 10^?3 to the maximum value of 12.0 × 10^?3 in the narrow x range from 0.040 to 0.055, then decreased to 3.2 × 10^?3 at x = 0.06. On the other hand, the η_(1 0 0) increases from 1.5 × 10^?3 to the maximum value of 2.9 × 10^?3 in the next narrow x range from 0.055 to 0.060. The variation of η_(1 0 0) differed in Li dependence from that of η_(0 1 1), which indicates that a large anisotropic strain remains in the crystal lattice in the PPB compositions.