Malaysian Journal of Analytical Sciences Vol 24 No 5 (2020): 766 - 771

 

 

 

 

EFFECT OF Cr2O3 ON THE TRANSITION TEMPERATURE AND PHASE FORMATION OF Tl2-xCrxBa2CaCu2O8-δ SUPERCONDUCTOR 

 

(Kesan Cr2O3 Terhadap Suhu Peralihan dan Pembentukan Fasa Superkonduktor Tl2-xCrxBa2CaCu2O8-δ)

 

Syahrul Humaidi1* and Roslan Abd-Shukor2

 

1Department of Physics,

FMIPA-Universitas Sumatera Utara, Jln Bioteknologi 1, Medan 20155, Indonesia

2Department of Applied Physics,

Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia

 

*Corresponding author:  syahrul1@usu.ac.id

 

 

Received: 13 November 2019; Accepted: 3 September 2020; Published: 12 October 2020

 

 

Abstract

The Tl-based high Tc superconductors, Tl2-xCrxBa2CaCu2O8-δ (Tl2212) have been prepared via the solid-state reaction method. The substitution of Cr into the Tl-site was aimed to investigate the role of Cr on the transition temperature and phase stability of the Tl2212 phase. Ba2CaCu2Oy precursor material was synthesized using BaCO3 (99.9%, Aldrich), CaO (99.99%, Alfa Aesar), and CuO (99.9%, Alfa Aesar) powder as the starting compound. The powders were mixed and sintered at 900 oC for 24 hours before cooled to room temperature. The precursor was mixed with Tl2O3 (99.9%, Alfa Aesar) and Cr2O3 (99.9%, Merck) powders before being pressed to obtain Tl2-xCrxBa2CaCu2O8 pellet. The pellets were heated at 900 oC with oxygen flow for 4 minutes. The transition temperature, Tc was determined using the standard four-point probe electrical resistance measurements from 50 K to 300 K with a constant current of 20 mA. The phases were determined by powder X-ray diffraction (XRD) method using CuKα source with λ= 1.5418 Å. Based on XRD analysis, the x = 0, 0.2, and 0.6 showed unit cell belonging to the 14/mmm space group. In the x = 0.4, the space group changed to P4/mmm which is the Tl1212 phase. It was found that the optimum composition was Tl1.8Cr0.2Ba2CaCu2O8-δ and the maximum zero-resistance temperature, Tc-zero was 96 K, and the onset temperature, Tc-onset was 116 K. It was observed that the transition temperatures decreased with increasing Cr2O3. The volume fraction of the Tl2212 phase in this composition was 88% with the c-lattice parameter equals to 29.388Å. Superconductivity was destroyed in the x = 1.0 samples.

 

Keywords:  transition temperature, structure, Tl2212 phase

 

Abstrak

Superkonduktor suhu tinggi berasaskan Tl iaitu, Tl2-xCrxBa2CaCu2O8-δ (Tl2212) telah disediakan melalui kaedah tindak balas pepejal. Penggantian Cr pada kedudukan Tl dilakukan untuk menyelidik peranan Cr terhadap suhu genting dan kestabilan fasa superkonduktor Tl2212. Bahan pelopor Ba2CaCu2Oy disintesis dengan menggunakan serbuk BaCO3(99.9%, Aldrich), CaO(99.99%, Alfa Aesar) dan CuO(99.9%, Alfa Aesar) sebagai campuran awal. Serbuk ini kemudiannya disinter pada 900 oC selama 24 jam dan dibiarkan sejuk sehingga suhu bilik. Bahan pelopor ini kemudianmya dicampurkan dengan serbuk Tl2O3 (99.9%, Alfa Aesar) dan serbuk Cr2O3(99.9%, Merck) untuk menghasilkan pelet Tl2-xCrxBa2CaCu2O8. Pelet kemudiannya disinter pada 900 oC dengan aliran gas oksigen selama 4 minit. Suhu peralihan, Tc ditentukan dengan pengukuran rintangan elektrik menggunakan kaedah piawai empat titik dalam suhu 50 K hingga 300K dengan bekalan arus malar 20 mA. Pecahan fasa diperolehi daripada kaedah pembelauan serbuk sinar-X (XRD) menggunakan sinar CuKα dengan panjang gelombang λ= 1.5418Å. Berdasarkan analisis XRD, sampel x = 0, 0,2, dan 0.6 adalah pada kumpulan ruang 14/mmm. Untuk sampel x = 0.4 kumpulan ruang berubah menjadi P4/mmm iaitu fasa yang berlainan (Tl1212). Didapati bahawa suhu peralihan sifar maksimum, Tc sifar adalah 96 K dan suhu perlalihan mula, Tc mula adalah 116 K bagi komposisi Tl1.8Cr0.2Ba2CaCu2O8-δ. Pecahan isipadu daripada fasa Tl2212 dalam sampel ini adalah 88% dengan parameter kekisi c bersamaan 29.388 Å. Sifat superkonduktor hilang pada komposisi x = 1.0. 

 

Kata kunci:  suhu peralihan, struktur, fasa Tl2212

 

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