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Home > Processing, Characterization, Structure and Ionic Conductivity of Disordered Pyrochlores, Ho2 Zryti1-Y 2O7 Holmium Zirconium-Titanate, Hzt

Processing, Characterization, Structure and Ionic Conductivity of Disordered Pyrochlores, Ho2 Zryti1-Y 2O7 Holmium Zirconium-Titanate, Hzt

Thesis Info

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Author

Shafique, Muhammad

Program

PhD

Institute

University of Peshawar

City

Peshawar

Province

KPK

Country

Pakistan

Thesis Completing Year

2008

Thesis Completion Status

Completed

Subject

Physics

Language

English

Link

http://prr.hec.gov.pk/jspui/bitstream/123456789/8131/1/Muhammad_Shafique_Physics_2017_UoP_Peshawar_22.06.2017.pdf

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676727018064

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In this study, a number of compounds in the Ho2(ZryTi1-y)2O7 pyrochlore system, which undergoes an order-disorder structural transition from pyrochlore to a defect-fluorite type, were investigated. The materials were processed by mechanical milling, followed by a two-step sintering route. The structure was analyzed via Rietveld refinements using neutron powder diffraction (NPD) data, and further supported by X-ray diffraction (XRD) to identify the phases and determine the composition of the pyrochlore-fluorite transformation boundary at room temperature. The NPD refinement and XRD results show that compositions with 0.0 ≤ y ≤ 0.5 crystallized into a pyrochlore structure while the ones with 0.7 ≤ y ≤ 1.0 crystallized into the defect-fluorite structure. The composition with y=0.6 was found to be a two phase (pyrochlore and defect-fluorite) mixture. Neutron refinement results confirmed that the cation disorder was independent of the anion Frenkel disorder and also the degree of Frenkel disorder O(1)-O(3) was different from the O(2)-O(3) anion disorder. The relation between x-parameter and anion Frenkel disorder was found to be linear for the pyrochlore structure. Unit-cell parameters were obtained using Rietveld refinements for the whole series and were also calculated via the Nelson-Riley function. The ionic conductivity studies were undertaken via AC impedance analysis to determine the electronic behaviour and its relationship to the structural change in the available temperature range of 300–700°C. The trends in ionic conductivity and activation energy were explained on the basis of NPD and XRD data. The composition at the pyrochlore-fluorite boundary exhibited the lowest activation energy and highest ionic conductivity.
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دل سے اک شخص کی یادوں کو رہا کرتے ہوئے
مر ہی جاوں نہ کہیں اس کو قضا کرتے ہوئے
تو کہ معبود سے نگران بھی سکتا ہے
میں نے سوچا ہی نہ تھا تجھ کو خدا کرتے ہوئے
ہاتھ اٹھاتے ہوئے وہم و گماں میں بھی نہ تھا
لب پہ اک نام جو آیا ہے دعا کرتے ہوئے
ہر کہانی کے قلم کار نے کیوں مار دیے
سارے کردار محبت میں وفا کرتے ہوئے
ہاتھ میں رنگ رکھا  ، باد صبا پر آنکھیں
پھول سے پھول کی خوشبو کو جدا کرتے ہوئے
شہر کا شہر ہی ویران نہ ہو جائے کہیں
میرے اک خواب کو تعبیر نما کرتے ہوئے
اب تو میں لوٹ کے جنگل میں نہیں جا سکتا
کھو گیا ہوں میں ترے گھر کا پتا کرتے ہوئے
تو کہے تو میں ترے دل سے نکل جاتا ہوں
میں نے جنت بھی چھوڑی تھی خطا کرتے ہوئے
آندھیوں سے تو مری جنگ نہیں ہے کوئی
شمع تو بجھنے نہ دی ذکر ہوا کرتے ہوئے
میں نے خیرات میں بھی پیار ہی مانگا ہے عدید
سوچتے کیا ہے سخی مجھ پہ عطا کرتے ہوئے

نکاح اور پاکستانی معاشرے میں شادی بیاہ کے مروجہ رسوم کا تحقیقی وتنقیدی جائزہ

The enlightened and moderated teachings of Islam empowered every one of the human society, specially the woman who used to be much oppressed in all civilizations of the world before emergence of Islam. Islam gave them an elevated status in all over the world in the status of mother, sisters, daughter and wife. It declared null and void the ignorance rules against them and, prohibited their sexual exploitation. Moreover, Islam gave a regular system of nikkah and marriages for women. The holy Prophet peace be upon him declared nikkah and marriage as his Sunnah and kept its procedure very simple. Furthermore,  he described marriage as a gigantic source of achieving chastity, but today in Pakistan the marriages have been made very complex and costly because of the   unIslamic customs and traditions. Those unIslamic customs became the part and parcel of the Pakistani marriages which not only made nikkah and marriage a difficult task but also devastated the economic, social and the religious life of Muslims. The Pakistani marriages are conducted with such customs of Mehndi, big congregations: Bharat, beating drums and singing songs. The article briefly discusses status of mirages in the pre Islamic era, Islamic concept and importance of nikkah and the new customs practiced in Pakistani marriages and their economic, social and religious impacts by best use of old and new resources.  

Synthesis and Properties of High-Temperature Thermoelectric Oxides for Efficient Energy Harvesting

The main goal of this research was to design and explore physical properties of high temperature thermoelectric oxide materials that are sufficiently thermally stable at high operating temperatures for power generation applications. Currently, the key challenges hampering the practical applications of thermoelectric power generators are the low efficiency, poor thermal stability, and high cost of thermoelectric materials. Metal oxide materials have recently grabbed a pronounced consideration owing to their low cost, non-toxicity, natural abundance of the constituting elements, and good thermal stability at high operating temperatures. Research work started with the investigation of ruthenium based Ba2−xBixCoRuO6 (0.0 ≤ x ≤ 0.6) double perovskite oxide materials. The polycrystalline samples were synthesized by solid-state reaction method and their crystal structures were characterized by the powder X-ray diffraction, and a combination of synchrotron X-ray and neutron powder diffraction data. Rietveld refinement analysis displays that all samples crystallize out in the hexagonal distorted crystal structure with P63/mmc space group. Scanning electron microscope (SEM) images reveal that Bi substitution results in increase of grain sizes due to lower melting point and hence faster diffusion-rate of Bi precursor at final heating temperature. The temperature dependent thermoelectric properties for all compounds depict semiconducting-like behavior and “small polaron hopping model” applies well with the temperature dependent electrical resistivity (ρ) and Seebeck coefficient (S) data. Moreover, Seebeck coefficient and thermal conductivity values significantly improve with increasing Bi-doping. The maximum thermoelectric power factor (PF) and figure of merit (zT) observed at 618 K for x = 0.6 specimen are 6.64 ´ 10-4 W/m·K2 and 0.23, respectively. We have also studied structural, magnetic and high-temperature thermoelectric properties of Sr2-xBixCoRuO6 (0 ≤ x ≤ 0.8) double perovskite oxide materials. Rietveld analysis of X-ray diffraction data shows that all samples adopt orthorhombic crystal structure with Immm space group. The electrical resistivity of all compounds exhibits semiconducting-like behavior. The Seebeck coefficient values change their sign from negative to positive with rising Bi-substitution after x = 0.2 sample. The maximum power factor and thermoelectric figure-of-merit (zT) obtained for Sr1.2Bi0.8CoRuO6 sample at 680 K are 1.87 ´ 10-4 W/m·K2 and 0.11, respectively.Substitution of metal cations with different size and charge at various crystallographic sites usually results in a significant improvement of thermoelectric properties of transition metal oxides. We have prepared dual doped Ca3−2xNa2xCo4−xMoxO9 (0 ≤ x ≤ 0.10) and Ca3−2xNa2xCo4−xWxO9 (0 ≤ x ≤ 0.075) misfit layered cobaltite samples by the traditional solid state reaction process. High temperature thermoelectric properties of these materials were measured and described in details in this document. The highest power factor obtained for Ca2.95Na0.05Co3.975Mo0.025O9 sample at 1000 K is 3.2 ´ 10-4 W/mK2. The corresponding figure-of-merit (zT) reaches a value of ~ 0.27 at 1000 K for this sample, which is ~3 times higher than the pristine Ca3Co4O9 system. A series of dual doped Bi2−2xNa2xSr2Co2−xWxOy (0 ≤ x ≤ 0.075) materials were prepared and their high temperature thermoelectric properties were investigated from room temperature to 1000 K. It was observed that dual substitution of Na, W in Bi2Sr2Co2Oy compound is very good approach in enhancing thermoelectric properties due to decrease of electrical resistivity and thermal conductivity concurrently of these materials. All specimens have a high Seebeck coefficient (S) and as a result a high thermoelectric figure of merit (zT) value of 0.35 at 1000 K was obtained for x = 0.025 specimen. In summary, doping of appropriate amounts of metal cations at various crystallographic sites of transition metal oxides results in decrease of electrical resistivity and thermal conductivity and increase the Seebeck coefficient values, which ultimately leads to a significant improvement in thermoelectric performance of these materials.