Wyniki wyszukiwania - BazTech

1

Dielectric relaxation and study of electrical conduction mechanism in BaZr0.1Ti0.9O3 ceramics by correlated barrier hopping model

Mondal T., Das S., Sinha T. P., Sarun P. M.

Materials Science Poland

|

2018

|

Vol. 36, No. 1

112--122

EN

This work aims to study the electrical conduction mechanism in the dielectric material BaZr0.1Ti0.9 O3 (BZT) ceramics by applying AC signal in the frequency range of 102 Hz to 106 Hz. The phase purity and microstructure of the sample have been studied by X-ray diffraction refinement and field-emission scanning electron microscope (FE-SEM) analysis. The appearance of resonance peaks in the loss tangent at high temperature is due to inherent dielectric relaxation processes of this oxide. The temperature dependent Cole-Cole plot has been studied in details to determine both the grain and grain boundary contribution to the conductivity. Electrical modulus analysis reveals that the hopping of charge carriers is the most probable conduction mechanism in BZT ceramics. The obtained data of AC conductivity obey the universal double power law and have been discussed in terms of microstructural network characteristics. The behavior of frequency exponent n of AC conductivity as a function of temperature verify the applicability of the correlated barrier hopping (CBH) model. The AC conductivity data are used to estimate the minimum hopping length, density of states at Fermi level, thermal conductivity and apparent activation energy. The value of activation energy confirms that the oxygen vacancies play a vital role in the conduction mechanism.

2

Correlation between structural, magnetic and spectroscopic properties of Mg substituted CoFe2O4

Nethala G. P., Tadi R., Anupama A. V., Shinde S. L., Veeraiah V.

Materials Science Poland

|

2018

|

Vol. 36, No. 2

310--319

EN

Mg substituted cobalt ferrite spinel powder samples with the general formula MgxCo1 – xFe2O4 (x = 0 to 0.25) were synthesized chemically through sol-gel method and annealed at 1100 °C for 2 h. They were initially screened for the structural and morphological properties by X-ray diffraction and field emission scanning electron microscopy, respectively. Vibrational properties of the samples were studied by Raman and infrared spectroscopies. X-ray diffraction confirmed the formation of single pure or near-pure phase with cubic spinel structure for all the samples with expected occupancy values. The field emission scanning electron microscopy revealed a decrease in the particle size with an increase in Mg concentration. Both structural and magnetic properties of the samples were characterized using Mössbauer spectroscopy while the magnetic properties were studied using vibrating sample magnetometry. The changes in magnetic moment of ions, their coupling with neighboring ions and cation exchange interactions were confirmed from the Mössbauer spectroscopy analysis. Saturation magnetization and coercivity values can be explained based on the Slater-Pauling curve. The magnetometry results showed a decrease in saturation magnetization of the samples with increase in Mg concentration.

3

Some aspects of the determination of retained austenite using the Rietveld refinement

Morawiec M.

Journal of Achievements in Materials and Manufacturing Engineering

|

2017

|

Vol. 80, nr 1

11--17

EN

Purpose: The aim of the paper is to show the advantage of the application of the Rietveld refinement for determination of retained austenite amount in multiphase microstructure steels. Design/methodology/approach: The steels used for the investigation were thermomechanically rolled and controlled cooled to room temperature. The investigation of the microstructure was carried out using light microscopy. X-ray diffraction investigations of analyzed steel were a major part of the research. The phase identification and quantitative analysis of retained austenite were done using the HighScore Plus software that includes the Rietveld refinement method. The Rietveld analysis takes into account the preferred orientation that occurs during thermo-mechanical processing of steel. Findings: It was found that after the thermo-mechanical processing the microstructure of steel is composed of fine-grained bainitic matrix which includes bainite-austenite constituents, martensite blocks and some fraction of retained austenite. The X-ray diffraction showed that this steel includes phases of Feα (bainite and martensite) and Feγ (retained austenite). The Rietveld analysis showed that the volume fraction of retained austenite is 14.1%. Research limitations/implications: To confirm that Rietveld refinement method is a good tool for the quantitative analysis of retained austenite volume fraction EBSD measurements should be done for comparison purposes. Practical implications: The obtained results can be used for determination of retained austenite fraction in AHSS steels. It is important because the retained austenite content and its mechanical stability decide about a formability level of these steel grades. Originality/value: Some methodological aspects are concerned affecting the final quantitative results of retained austenite volume fraction is AHSS.

4

Structural determination of Co/TiO2 nanocomposite: XRD technique and simulation analysis

Mostaghni F., Abed Y

Materials Science Poland

|

2016

|

Vol. 34, No. 3

534--539

EN

Synthesis and complex theoretical and experimental studies of Co/TiO2 anatase have been reported. The preparation of Co/TiO2 was carried out by sol-gel method. Distribution of cations among the two tetrahedral and octahedral sites was estimated by analyzing the powder X-ray diffraction patterns by employing Rietveld refinement technique, and the results revealed the existence of tetragonal structure. Band structure and density of states calculations were performed using the first-principles methods. The structural and electronic properties of Co/TiO2 were calculated in the general gradient approximation (GGA). An additional comparison with pure TiO2 anatase allowed us to clarify cobalt doping effect on the electronic structure and the band gap. The band gap of Co/TiO2 was decreased by broadening the valence band as a result of the overlap among Co 3d, Ti 3d, and O 2p states, which made it respond better to visible and solar light.

5

Conventional synthesis and characterization of rare earth doped barium borophosphates, BaBPO5:RE (Y, Gd and La)

Çelik Gül G., Kurtuluş F.

Archives of Materials Science and Engineering

|

2016

|

Vol. 81, nr 2

49--54

EN

Purpose: of this research, our target is synthesis and characterization of rare earth metals such as Y, Gd and La doped barium borophosphate compounds which are applicable in non-linear optics industry. Design/methodology/approach: The starting materials rare earth oxides, barium carbonate, boric acid and ammonium dihydrogen phosphate as analytically grade weighed 0.01:1:1:1 molar ratio and homogenized in an agate mortar. The mixture placed into a porcelain crucible to heat in high temperature oven step by step. First, mixtures were waited at 400°C for 2 hours for calcination process, subsequently heated 900°C with step rate 10°C/m for 8 hours, and finally cooled down to room temperature with step rate 10°C/m. After many grindings final product get ready for characterization. X-ray powder diffraction (XRD) analysis was performed using PANanalytical X’Pert PRO Diffractometer (XRD) with Cu Kα (1.5406 Å, 45 kV and 30 mA) radiation. Fourier transform infrared spectroscopy (FTIR) was taken on a Perkin Elmer Spectrum 100 FTIR Spectrometer from 4000 to 650 cm-1. Scanning electron microscopy was achieved in SEM JEOL 6390-LV. Luminescence properties were performed by Andor Solis Sr 500i spectrophotometer. Conventional solid state syntheses were done in Protherm furnace. Findings: The powder XRD patterns of the samples show that there is no impurity related to doping materials mean all diffractions corresponding to host material barium borophosphate crystallized in hexagonal system with unit cell parameters a=7.1003 and c=6.9705 Å. The unit cell parameters of rare earth doped barium borophosphates were calculated and display both increase and decrease depends on ionic Radius of rare earths. The other supporting methods confirm the crystal structure and luminescence properties. Research limitations/implications: The synthesis method has some disadvantages such as low homogeneity, non-uniform product etc. We tried to minimize these negative aspects in our research and succeeded. Practical implications: Phosphor materials Y:BaBPO5, Gd:BaBPO5 and La:BaBPO5 (ICSD 51171) were synthesized by conventional solid state method and characterizations was mainly based on powder X-ray diffraction pattern. Also, morphological and luminescence properties were completed to get the highest knowledge. Originality/value: Of the paper is first time conventional synthesis of Y, Gd and La doped BaBPO5 compounds, calculation of unit cell parameters, and investigation of morphological and luminescent properties.

6

Structure studies on the AK7-SiC composite after machining

Karolus M., Cyboroń J., Putyra P., Dyzia M., Ratuszek W.

Mechanik

|

2015

|

R. 88, nr 2CD

319--329

EN

The paper presents results of the structural studies on the composites of alumina matrix after machining processes. There were used two different methods: Electrical Discharge Machining (EDM) and Abrasive Water Jet (AWJ). The phase composition of the composite was carried out by X-ray diffraction (XRD). In order to investigate the heterogeneity of the material there were conducted additional measurements using the Grazing Incident X-ray Diffraction (GIXD) for angles of 1°, 3°, 5°, 9° and 12°. Residual stresses were determined based on the sin2ψ and grazing (g-sin2ψ) methods for the main components of the composite - alumina and silicon carbide. Analysis of the diffraction patterns performed for different X-ray penetration depths, showed that the tested material was inhomogeneous. Furthermore, depending on the treatment method (EDM or AWJ), the tested materials were shown the differences, both in the phase composition and the residual stresses values, as well.

PL

W pracy przedstawiono wyniki badań strukturalnych stopów z układu AK7-10% obj. SiC, po procesie obróbki ubytkowej z wykorzystaniem dwóch metod: elektroerozyjnej i wodnościernej. Badania składu fazowego oraz jego zmian przeprowadzono metodą dyfrakcji rentgenowskiej (XRD) w geometrii Bragga-Brentano. W celu zbadania niejednorodności materiału przeprowadzono dodatkowe pomiary w geometrii stałego kata padania (SKP – Grazing Incident X-ray Diffraction) dla kątów padania promieniowania rentgenowskiego: 1°, 3°, 5°, 9°, 12°. Przeprowadzono pomiary naprężeń własnych dla głównych składników stopów, tj. Al i SiC, które wyznaczono w oparciu o metodę g-sin2ψ. Analiza dyfraktogramów wykonanych przy różnych głębokościach wnikania promieniowania rentgenowskiego wykazała, iż badany materiał kompozytowy jest wielofazowy i niejednorodny. Ponadto, w zależności od zastosowanej metody obróbki badanych materiałów (EDM i obróbka wodnościerna), wystąpiły różnice, zarówno w składzie fazowym, jak i w wielkościach wyliczonych naprężeń własnych.

7

Synthesis and crystal structure of chlorate-enclathrated in aluminogermanate sodalite Na8[AlGeO4]6(ClO3)2

Borhade A. V., Dholi A. G.

Materials Science Poland

|

2013

|

Vol. 31, No. 2

246--252

EN

Encapsulation of chlorate in sodalite with aluminogermanate host framework has been obtained by one pot hydrothermal synthesis at 393 K. The crystal structure of Na8[AlGeO4]6(ClO3)2; sodalite was refined from X-ray powder data in the space group P43n: a = 9.169 Å, where Al-O-Ge angle is 137.6. The 27Al MAS NMR study confirmed alternate Ge and Al ordering of the sodalite framework, while 23Na gave insight into the structure and dynamics of the cage fillings. Infrared spectrum confirmed the encapsulation of chlorate as well as the framework formation of aluminogermanate sodalite. SEM study showed the retention of cubical morphology of the aluminogermanate sodalite. Thermogravimetric analysis provided information on the extent of chlorate entrapment, stability within the sodalite cages and decomposition properties.

8

Synthesis and characterization of aluminosilicate and gallosilicate sodalites containing acetate ions

Borhade A. V., Wakchaure S. G.

Materials Science Poland

|

2011

|

Vol. 29, No. 2

127--134

EN

One pot synthetic aluminosilicate and gallosilicate sodalites containing acetate guest anion have been synthesized successfully under hydrothermal conditions at 100 °C. This paper deals with the comparison of X-ray powder data with single crystal data for Na8[AlSiO4]6(CH3COO)2 and the characterization of a new Na8[GaSiO4]6(CH3COO)2 sodalite. The products obtained were characterized by IR, X-ray powder diffraction, MAS NMR, SEM and thermogravimetry technique. Crystal structures were refined in the space group P?43n from X-ray powder data using the Rietveld refinement method with the unit cell parameter a = 9.0679 A° , for aluminosilicate and a = 9.2119 A° , for gallosilicate sodalite. The aluminosilicate and gallosilicate framework shows regular bonding with bond angles of Al-O-Si = 146.241°, Ga-O-Si = 141.294°. 29Si MAS NMR chemical shift values verify Al/Si and Ga/Si ordering of the framework constituents.

9

Structure studies on nanocrystalline powder of MgO xerogel prepared by the sol-gel method

Dercz G., Prusik K., Pajak L., Pielaszek R., Jmalinowski J. J., Pudlo W.

Materials Science Poland

|

2009

|

Vol. 27, No. 1

201--207

EN

Structure studies were performed on nanocrystalline powder of MgO xerogel prepared by the sol-gel technique, producing high purity, chemically homogeneous materials of relatively high specific surface area. Magnesium methoxide was used as an MgO precursor. The wet gel was dried under conventional conditions, yielding xerogel with periclase phase; the only crystalline form of magnesium oxide. The X-ray diffraction, scanning and transmission electron microcopies were used as the tools of structure analysis. The Toraya PRO-FIT procedure and the Rietveld refinement method were applied for X-ray data analysis. Both techniques apply the Pearson VII function for the description of line profiles. The gamma crystallite size distribution was determined using the FW(1/5)/(4/5)M method proposed by Pielaszek. The obtained values of and ? (measure of polydispersity) of particle size parameters are equal to 7.1 nm and 2.1 nm, respectively, whereas the average crystallite size, estimated by the Williamson- Hall procedure, was equal to 7.5 nm. The Rwp, and S fitting parameters obtained from the Rietveld refinement were equal to 6.4% and 1.8, respectively. This would seem the most satisfactory result, when considering the nanosize of MgO crystallites and a very probable presence of amorphous phase.

10

Ordering process of Fe28Al and Fe28Al5Cr alloys

Pająk L., Kansy J., Hanc A., Dercz G., Jabłońska M.

Archives of Materials Science and Engineering

|

2008

|

Vol. 30, nr 2

81-84

EN

Purpose: The comparison of ordering process in Fe28Al and Fe28Al5Cr alloys annealed for 8, 16 and 48 hours at 1000°C was performed. The composition of studied alloys is closed to one of Fe3Al phase. Design/methodology/approach: The studied alloys were melted in induction furnace under vacuum. Next the alloys were gravitatively casted into cylindrical graphite moulds. The alloy samples were annealed at 1000°C for 8, 16 and 48 hours. The ordering process was analyzed by X-ray diffraction,Mössbauerspectroscopy and positron annihilation methods. Findings: Different behaviour of Fe28Al and Fe28Al5Cr alloys during annealing for 8, 16 and 48 hours at 1000°C was found. The Fe3Al phase of DO3 type structure was stated only in the sample of Fe28Al alloy annealed for 48 hours. The FeAl phase appeared to be the main phase in the other samples. Research limitations/implications: The applied investigation methods appeared to be useful in the studies of long range ordering process. Application of Rietveld refinement method enabled the verification of qualitative phase analysis and the determination of lattice constant parameters. Relatively great grain sizes in studied samples made the exact determination of long range ordering parameters difficult. Practical implications: The information on the phase transformation during the heat treatment of alloys, including long range ordering, are of prime importance for technological processing. The structures with long range ordering significantly affect the properties of alloys with intermetallic phases. Originality/value: Good correlation between the results of X-ray diffraction, Mossbauer spectroscopy and positron annihilation methods were obtained. Addition of chromium made the long range ordering process slower.

11

Rozpraszanie dyfuzyjne i metoda Rietvelda w badaniach materiałów nanokrystalicznych

Karolus M., Łągiewka E.

Archiwum Nauki o Materiałach

|

1999

|

T. 20, nr 4

207-239

PL

Niniejsza praca ma charakter metodyczny i jej podstawowym celem jest opracowanie procedury pozwalającej na wspólne wykorzystanie metody RDF i metody Rietvelda do opisu modelu budowy materiałów nanokrystalicznych wykazujących rentgenowski obraz dyfrakcyjny, tak jak materiały amorficzne, oraz określenie warunków stosowalności połączenia tych metod. Opierając się na analizie dyfuzyjnego rozpraszania promieniowania rentgenowskiego, na przykładzie nanokrystalicznych stopów Cu-Cd wykreślono funkcje RDF, z których wyznaczono wartości promieni i liczb koordynacyjnych, a także przybliżony model struktury. Korzystając z tych danych zastosowano procedurę Rietvelda, w której zmieniając takie wielkości jak: współczynniki dopasowania tła, funkcje opisujące kształt i szerokość połówkową linii dyfrakcyjnej, parametry komórki elementarnej, współrzędne położenia atomów, parametry obsadzeniowe (POP) i temperaturowe, wykreślano dyfraktogram teoretyczny i porównywano go z eksperymentalnym aż do otrzymania najlepszego dopasowania, tj. do uzyskania najmniejszych wartości czynników R. Uzyskane ostatecznie parametry budowy badanych materiałów posłużyły do wyrysowania modeli hipotetycznych "komórek elementarnych" badanych stopów. W pracy wykazano, że taki sposób postępowania dla materiałów nanokrystalicznych jest możliwy i prowadzi do określenia najbardziej prawdopodobnego modelu ich budowy. Z tego względu w podsumowaniu podano kolejne etapy realizacji zaproponowanej procedury.

EN

The aim of this paper was to prepare the procedure connecting the Radial Distribution Function Method and The Rietveld Refinement Method to study the nanocrystalline structure model. The conditions for applying these two methods were also studied. On the basis of the Radial Distribution Function obtained for nanocrystalline Cu-Cd alloys, the coordination numbers and radii of coordination spheres were determined. These results led to the first approximation of the model structure. Then the Rietveld Refinement Method was used to obtain the more likely model structure. The background, shape and FHWM of the diffraction line, parameters of unit cell x, y, z-parameters and POP parameters were refined during the whole procedure. The final results of Rietveld Refinement were used as the base for drawing the structure model of the hypothetical "unit cell". It was shown that the procedure described in this paper may be applied for selecting the most probable model structure of nanocrystalline materials.