scholarly journals Investigations of nano-crystalline Sr0.5Ba0.5Nb2O6 and bulk ceramics synthesized by a polymerization method using PEG400

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Optical Band Gap ◽  
Linear Thermal Expansion Coefficient ◽  
Sintering Temperature ◽  
Linear Thermal Expansion ◽  
Dielectric Measurements ◽  
One Pot ◽  
Grain Sizes ◽  
Nano Crystalline ◽  
Polymerization Method ◽  
Diffuse Phase

Nano-crystalline Sr0.5Ba0.5Nb2O6 was synthesized by a one-pot method using PEG400 and citric acid. Calcination of the (Sr,Ba,Nb)-gel at 600 °C leads to Sr0.5Ba0.5Nb2O6with a crystallite size of 24(2) nm and a specific surface area of 38.5(10) m2 g-1. Sintering up to 1325 °C leads to ceramics with globular or irregular-shaped grains and average grain sizes between 1.3 and 2.4 μm, whereas higher temperatures lead to a rod-like microstructure. Theindirect allowed optical band gap varies between 3.70(5) and 3.29(5) eV. Dielectric measurements show a diffuse phase transition and weak relaxor properties. The maximum of the permittivity occurs between 116 and 147 °C. The frequency dependence of the impedance can be well described by one or two RC-circuits depending on sintering temperature. The melting temperature is determined as 1506(7) °C with dHf = 140(20) kJ mol-1. The average linear thermal expansion coefficient is found to be 10.5(5)^10-6 K-1.

Effect of Sintering Temperature on Dielectric Properties of CaCu3Ti4O12 Ceramics Prepared by Mechanochemical Process

2014 ◽  
Vol 974 ◽  
pp. 157-161
Author(s):  
Masturah Mohamed ◽  
Mahesh Talari ◽  
Mohd Salleh Mohd Deni ◽  
Azlan Zakaria
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Sintering Temperature ◽  
Processing Conditions ◽  
Dielectric Measurements ◽  
Frequency Range ◽  
Grain Sizes ◽  
Barrier Capacitance ◽  
Different Temperatures ◽  
Increasing Temperature

CaCu3Ti4O12(CCTO) is well known to have colossal dielectric constant in the range of 105.It is widely accepted that this phenomenon may be attributed to internal layer barrier capacitance (IBLC) model. The dielectric properties of CCTO were reported to be strongly dependent on the processing conditions and grain size. In this work, CCTO samples with different grain sizes were produced by varying sintering temperature in order to investigate IBLC effect on dielectric properties of CCTO. The samples were sintered at four different temperatures, (T=1100°C, 1050°C, 1000°C and 950°C). Dielectric measurements were carried out for the samples in the frequency range of 102– 106Hz using impedance spectrometer. Electron micrographs showed that increasing temperature promoted the grain growth of CCTO while sintering. The internal crystalline defects are seen to play major role by increasing the grain conductivity in dipole formation and increased the dielectric constant of the samples.

scholarly journals Magnetic, optical, dielectric, and sintering properties of nano-crystalline BaFe0.5Nb0.5O3 synthesized by a polymerization method

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Crystallite Size ◽  
Magnetic Measurements ◽  
Spontaneous Magnetization ◽  
Secondary Phase ◽  
Phase Evolution ◽  
One Pot ◽  
Nano Crystalline ◽  
Rc Circuit ◽  
Tan Δ ◽  
Polymerization Method

Full text also available at: http://rdcu.be/v7Fn A one-pot polymerization method using citric acid and glucose for the synthesis of nano-crystalline BaFe0.5Nb0.5O3 is described. Phase evolution and the development of the crystallite size during decomposition of the (Ba,Fe,Nb)-gel were examined up to 1100 °C. Calcination at 850 °C of the gel leads to a phase-pure nano-crystalline BaFe0.5Nb0.5O3 powder with a crystallite size of 28 nm. The shrinkage of compacted powders starts at 900 °C. Dense ceramic bodies (relative density ≥ 90%) can be obtained either after conventional sintering above 1250 °C for 1 h or after two-step sintering at 1200 °C. Depending on the sintering regime, the ceramics have average grain sizes between 0.3 and 52 μm. The optical band gap of the nano-sized powder is 2.75(4) eV and decreases to 2.59(2) eV after sintering. Magnetic measurements of ceramics reveal a Neel temperature of about 23 K. A weak spontaneous magnetization might be due to the presence of a secondary phase not detectable by XRD. Dielectric measurements show that the permittivity values increase with decreasing frequency and rising temperature. The highest permittivity values of 10.6 9 104 (RT, 1 kHz) were reached after sintering at 1350 °C for 1 h. Tan δ values of all samples show a maximum at 1–2 MHz at RT. The frequency dependence of the impedance can be well described using a single RC-circuit.

scholarly journals Thermal Properties of Stabilized Zirconia at Low Temperatures

1985 ◽  
Vol 38 (4) ◽  
pp. 617 ◽  
Author(s):  
JG Collins ◽  
SJ Collocott ◽  
GK White
Keyword(s):  
Heat Capacity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Low Temperatures ◽  
Linear Thermal Expansion Coefficient ◽  
Linear Thermal Expansion ◽  
Stabilized Zirconia ◽  
Elastic Data

The linear thermal expansion coefficient a from 2 to 100 K and heat capacity per gram cp from 0�3 to 30 K are reported for fully-stabilized zirconia containing a nominal 16 wt.% (9 mol.%) of yttria. The heat capacity below 7 K has been analysed into a linear (tunnelling?) term, a Schottky term centred at 1�2 K, a Debye term (e~ = 540 K), and a small T5 contribution. The expansion coefficient is roughly proportional to T from 5 to 20 K and gives a limiting lattice Griineisen parameter 'Yo ::::: 5, which agrees with that calculated from elastic data.

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

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Thermal Expansion ◽  
Low Temperature ◽  
Growth Process ◽  
Optical Band Gap ◽  
High Specific Surface Area ◽  
Crystallite Growth ◽  
Crystalline Powder ◽  
Aqueous Synthesis ◽  
Nano Crystalline ◽  
Naoh Solution

A facile method to prepare nanoscaled BaFe0.5Nb0.5O3 via synthesis in boiling NaOH solution is describedherein. The nano-crystalline powder has a high specific surface area of 55 m2 g−1 and a crystallite sizeof 15 nm. The as-prepared powder does not show any significant crystallite growth up to 700 ◦C. Theactivation energy of the crystallite growth process was calculated as 590 kJ mol−1. Dense ceramics can beobtained either after sintering at 1200 ◦C for 1 h or after two-step sintering at 1000 ◦C for 10 h. The averagegrain sizes of ceramic bodies can be tuned between 0.23 µm and 12 µm. The thermal expansion coefficientwas determined as 11.4(3)·10−6 K−1. The optical band gap varies between 2.90(5) and 2.63(3) eV. Magneticmeasurements gave a Néel temperature of 20 K. Depending on the sintering regime, the ceramic samplesreach permittivity values between 2800 and 137,000 at RT and 1 kHz.

scholarly journals BaGeO3 as sintering additive for BaTiO3-MgFe2O4 composite ceramics

2019 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Magnetic Measurements ◽  
Sol Gel ◽  
Dissipation Factor ◽  
Composite Ceramics ◽  
Composite Powders ◽  
One Pot ◽  
Fine Grained ◽  
Sintering Additive ◽  
Nano Crystalline ◽  
Sintering Behaviour

BaTiO3-MgFe2O4 composites (30 wt.% MgFe2O4) with a small addition of BaGeO3 as a sintering additive were synthesized by a one-pot Pechini-like sol-gel process. Nano-crystalline composite powders with a crystallite size of about 10 nm were obtained after reaction at 700 °C for 1 h. Magnetic investigations suggest that the nano-powder is in its superparamagnetic state at room temperature. The addition of BaGeO3 leads to an improved sintering behaviour. DTA measurements reveal the formation of a liquid phase at 1164(3) °C. Dense ceramic bodies (relative density > 90 %) were obtained after sintering for 1 h at 1150 °C. SEM investigations prove a 0-3 connectivity and show that the addition of BaGeO3 promotes the grain growth leading to particles up to 4 μm. In contrast, fine-grained composite ceramics with smaller particles up to 230 nm were obtained after a two-step sintering process. Magnetic measurements indicate a ferrimagnetic behaviour with coercivity values up to 70 Oe depending on the sintering procedure. Furthermore, addition of BaGeO3 results in an increase of the relative permittivity, whereas the dissipation factor slightly decreases.

Electrical Conductivity Measurements of Al-Doped ZnO Semiconductor in High Temperature

2018 ◽  
Vol 772 ◽  
pp. 105-109
Author(s):  
Syamsul Hadi ◽  
Husein Jaya Andika ◽  
Agus Kurniawan ◽  
Suyitno
Keyword(s):  
Electrical Conductivity ◽  
Temperature Effects ◽  
Sintering Temperature ◽  
High Porosity ◽  
Conductivity Measurements ◽  
Grain Sizes ◽  
Lower Porosity ◽  
Doped Zno ◽  
Zno Semiconductor ◽  
Zno Doping

Electrical conductivity plays an important role in the performance of thermoelectric semiconductor material. This study discusses the electrical conductivity measurements of Zinc Oxide (ZnO) doping Aluminium (Al) pellet as a material of thermoelectric using four-point probe method at high temperatures. Al-doped ZnO (2 wt%) pellet was sintered at the temperature of 1100°C, 1200°C, 1300°C, 1400°C, and 1500°C with the heating rate of 8°C/minute. SEM and XRD tests show that the higher sintering temperature effects to larger grain sizes, better crystallinity, and lower porosity. There is no electrical conductivity in the sintering sample at 1100°C due to the small grain sizes and high porosity. In the sintering sample at 1500°C, the phase of ZnAl2O4erupted. The highest electrical conductivity of 5923.48S/m of Al-doped ZnO pellet was obtained at the sintering temperature of 1400°C with measurement temperature of 500°C.

Effect of the Isotopic Composition of Fe on Its Linear Thermal Expansion Coefficient

2021 ◽  
Vol 57 (11) ◽  
pp. 1135-1139
Author(s):  
Yu. S. Belozerov ◽  
A. V. Knyazev ◽  
B. N. Kodess ◽  
A. S. Shipilova ◽  
M. O. Steshin ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Isotopic Composition ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Linear Thermal Expansion Coefficient ◽  
Linear Thermal Expansion

Low-Melting Glass-Ceramic Composites with Low Linear Thermal Expansion Coefficient for Radio-Electronics

2015 ◽  
Vol 756 ◽  
pp. 313-318 ◽  
Author(s):  
Valeriy M. Pogrebenkov ◽  
Kirill S. Kostikov ◽  
E.A. Sudarev ◽  
A.V. Elistratova ◽  
Ksenia S. Kamyshnaya ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Glass Ceramic ◽  
Ceramic Composite ◽  
Linear Thermal Expansion Coefficient ◽  
Linear Thermal Expansion ◽  
Ceramic Composites ◽  
Radio Electronics ◽  
Glass Ceramic Composite

Glass-ceramic composite materials based on lead-borate glass and eucryptite – a compound with a negative coefficient of linear thermal expansion (CTE), along with the conditions for their production are studied in this paper. Effects of the amount and granulometric composition of the eucryptite as well as time/temperature processing conditions on the change of the linear thermal expansion coefficient of the sintered samples are also examined.

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