• R N P Choudhary

Articles written in Bulletin of Materials Science

• Phase transitions in Na2TeO4 ceramics

Polycrystalline samples of NaTeO4 were prepared by conventional solid-state reaction technique at low temperature (600° C). X-ray powder diffraction (XRD) technique was used to check the formation of single phase NaTeO4 compound with cell parametersa = 10·602(1) åb = 70·622(1) å andc = 8·506(1) å in orthorhombic crystal system. Detailed studies of dielectric constant (ε) (and loss tangent (tan δ) as a function of frequency (400 Hz-10 kHz) and temperature (−120°C–260°C) show that the compound has two phase transitions in the ferroelectric phase.

• Synthesis, structure and characterization of ceramic Ca4Bi2Ti4Nb6O30

The polycrystalline samples of Ca4Bi2Ti4Nb6O30 (herein designated CBTN) were synthesized by the conventional ceramic method. Preliminary X-ray structural study of the compound showed the formation of a single phase solid solution having orthorhombic structure in the paraelectric phase. Measurements of the dielectric constant (𝜀') and dielectric loss (tan 𝛿) as a function of temperarure (-180-200°C) at 1 kHz and 10 kHz and also as a function of frequency (102 Hz to 104 Hz) at five different temperatures [-180°C, -40°C, -10°C, 26°C (room temperature) and 75°C] have shown a dielectric anomaly and a phase transition at -13 ± 1°C in CBTN.

• Structural, dielectric and electrical properties of Sm-modified Pb(SnTi)O3 ferroelectric system

We have synthesized (Pb1–𝑥Sm𝑥)(Sn𝑦Ti1–𝑦)1–𝑥/4O3 (PSmST) polycrystalline ferroelectric ceramics with 𝑥 = 0.05, 0.07, 0.1 and 𝑦 = 0.45 by a solid-state reaction technique and performed preliminary X-ray diffraction (XRD) analysis, detailed temperature and frequency dependence dielectric measurements on them. The a.c. conductivity has been investigated over a wide range of temperature and the activation energy ($E_{a.c.}$) has also been calculated. It is observed that

the dielectric permittivity (𝜀) and loss tangent (tan 𝛿) are dependent on frequency,

the temperature of dielectric permittivity maximum shifts toward lower temperature side with the increase of samarium ion (Sm+3) concentration at the Pb sites, and

observed and calculated 𝑑-values of XRD patterns show that the compounds have been formed in orthorhombic single phase.

• Impedance analysis of Pb2Sb3LaTi5O18 ceramic

Polycrystalline sample of Pb2Sb3LaTi5O18, a member of tungsten–bronze (TB) family, was prepared using a high temperature solid-state reaction technique. XRD analysis indicated the formation of a singlephase orthorhombic structure. The dielectric studies revealed the diffuse phase transition and the transition temperature was found to be at 52°C. Impedance plots were used as tools to analyse the sample behaviour as a function of frequency. Cole–Cole plots showed Debye relaxation. The activation energy was estimated to be 0.634 eV from the temperature variation of d.c. conductivity. The nature of variation of d.c. conductivity with temperature suggested NTCR behaviour.

• Synthesis and structural characterization of some Pb(B$^{'}_{1/3}$Nb2/3)O3 type materials by two-stage solid-state route

Two-stage columbite solid state reaction route has been used for the preparation of Pb (B$^{'}_{1/3}$Nb2/3)O3 materials (B′ = Mg, Ni and Cd). The columbite precursor phase was structurally characterized using diffraction data. MgNb2O6, NiNb2O6 and CdNb2O6 show orthorhombic structures i.e. pure columbite phase. Final phase materials get stabilized in mixed phase. The diffraction pattern shows that it is a mixture of cubic pyrochlore and perovskite phase. Percentage of perovskite phase was calculated using the band intensities of (110) perovskite and (222) pyrochlore peaks. The calculated percentages show the dominant perovskite phase. Possible reasons for mixed phase are discussed.

• Impedance spectroscopy of Ba3Sr2DyTi3V7O30 ceramic

Polycrystalline sample of Ba3Sr2DyTi3V7O30 was prepared at 950°C using a high-temperature solid-state reaction technique. X-ray structural analysis indicated the formation of a single-phase orthorhombic structure with lattice parameters: 𝑎 = 12.2719 (39) Å, 𝑏 = 8.9715(39) Å and 𝑐 = 19.7812(39) Å. Microstructural study showed densely packed uniform distribution of grains over the surface of the sample. The a.c. impedance plots were used as tools to analyse the electrical response of the sample as a function of frequency at different temperatures (30–500°C). These plots revealed the presence of grain boundary effect, from 200°C onwards. Complex impedance analysis showed non-Debye type of dielectric relaxation. The Nyquist plots showed the negative temperature coefficient of resistance character of Ba3Sr2DyTi3V7O30. A hopping mechanism of electrical transport processes in the system is evident from the modulus analysis. The activation energy of the compound (calculated both from loss and modulus spectrum) is the same, and hence the relaxation process may be attributed to the same type of charge carrier.

• Electrical and magnetic properties of (BiNa)1/2(FeV)1/2O3

Potential multiferroic material, (BiNa)1/2(FeV)1/2O3, synthesized using solid-state route is investigated. The phase formation was confirmed by X-ray diffraction and surface morphology by scanning electron microscopy (SEM). Structural data reveal the single phase formation corroborated by SEM. The grain distribution is uniform with an average grain size of 3.6 𝜇m. Electrical properties were investigated in a frequency range (1 kHz–1 MHz) by complex impedance spectroscopy (CIS) technique. The material showed negative temperature coefficient of resistance (NTCR) reflecting semiconductor behaviour. A.C. conductivity was found to obey Johnscher’s law. Conductivity mechanism is discussed and activation energy estimated (1.17 eV) for the conduction process is associated with Fe3+ → Fe2+ variable state. The M–H curve showed the presence of ferromagnetism in the studied material.

• Structural, dielectric and electrical properties of Li2Pb2La2W2Ti4Nb4O30 ceramic

Li2Pb2La2W2Ti4Nb4O30 complex ferroelectric oxide was prepared by using a high-temperature solidstate reaction method (calcination temperature, ∼1100 °C and sintering temperature, ∼1150 °C). Room temperature preliminary structural analysis shows formation of a single-phase compound. The nature of microstructure (i.e. grain distribution, presence of voids, grain size, etc) recorded using scanning electron microscope (SEM) clearly suggests the formation of high quality and density of pellet samples. Studies of temperature dependence of dielectric constant, tangent loss and polarization show the existence of ferroelectric phase transition in the material at high temperature (307 °C). Detailed studies of temperature dependence of electrical parameters (i.e. impedance (400−475 °C),modulus, conductivity, etc) of the material clearly suggest a strong correlation between itsmicrostructure (i.e. bulk, grain boundary, etc) and electrical properties. The nature of temperature variation of d.c. conductivity showed an Arrhenius behaviour of the material. A signature of ionic conductivity in the material was observed in its a.c. conductivity spectrum. The nature of frequency dependence of a.c. conductivity of the material can be explained by Jonscher’s universal power law. Electrical transport properties of the material show existence of non-exponential type of conductivity relaxation.

• # Bulletin of Materials Science

Volume 45, 2022
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020