Sains Malaysiana 51(9)(2022): 3095-3101

http://doi.org/10.17576/jsm-2022-5109-28

Atenuasi Ultrasonik dan Modulus Ricih pada Suhu Genting Superkonduktor Terdop Sederhana (Tl_0.8Bi_0.2)Sr₂(Ca_0.9Cr_0.1)Cu₂O₇

(Ultrasonic Attenuation and Shear Modulus at the Critical Temperature of Moderately Doped

(Tl_0.8Bi_0.2)Sr₂(Ca_0.9Cr_0.1)Cu₂O₇ Superconductor)

R. ABD-SHUKOR^1,*, L.K. TAN¹, NOR AZAH NIK-JAAFAR² & M.N. MOHD NASIR¹

¹Department of Applied Physics, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia

²Pusat GENIUS@Pintar Negara, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia

Received: 5 March 2021/Accepted: 14 June 2022

Abstrak

Modulus ricih dan atenuasi ultrasonik superkonduktor suhu tinggi terdop sederhana (Tl_0.8Bi_0.2)Sr₂(Ca_0.9Cr_0.1)Cu₂O₇ (Tl-1212) dengan suhu genting (T_c ) 98 K telah dikaji.  Modulus ricih, G meningkat apabila suhu diturunkan daripada 240 K ke 80 K yang menunjukkan pengerasan kekisi.  Walau bagaimanapun, pada suhu antara 160 K hingga 190 K modulus ricih menunjukkan anomali menandakan kecenderungan untuk kekisi melembut.  Berhampiran suhu genting modulus ricih menunjukkan pelembutan kekisi iaitu ketakselanjaran pada cerun (dG/dT) dan ini sejajar dengan ciri peralihan fasa termodinamik tertib ke dua.  Peratus perubahan modulus ricih antara 240 K dan 80 K ialah 5.5%.  Atenuasi ultrasonik menunjukkan penurunan mendadak daripada 240 K ke 210 K diikuti dengan profil yang hampir mendatar sehingga 140 K.  Puncak atenuasi dicerap berhampiran suhu genting dan ini menunjukkan penyerapan tenaga akustik meningkat apabila bahan memasuki fasa mensuperkonduksi.  Anomali modulus ricih dan atenuasi ultrasonik ini dijelaskan melalui peralihan fasa tertib kedua dan tertiban oksigen jarak dekat dalam satah Cu-O unit sel bahan superkonduktor ini.

Kata kunci: Getaran kekisi; mikrostruktur; peralihan fasa; sifat akustik

Abstract

The shear modulus and ultrasonic attenuation of a moderately doped (Tl_0.8Bi_0.2)Sr₂(Ca_0.9Cr_0.1)Cu₂O₇ (Tl-1212) high temperature superconductor with critical temperature (T_c) of 98 K have been studied.  The shear modulus, G increased when the temperature was lowered from 240 K to 80 K indicating lattice hardenings. However, at temperatures between 160 K and 190 K, the shear modulus showed an anomaly indicating a lattice softening tendency.  Near the critical temperature the shear modulus showed lattice softenings i.e., a discontinuity in the slope (dG/dT) and this is consistent with the characteristic of a second-order thermodynamic phase transition.  The percent change in shear modulus between 240 K and 80 K was 5.5 %.  Ultrasonic attenuation showed a sharp decrease from 240 K to 210 K followed by a near horizontal profile to 140 K.  An attenuation peak was observed near the critical temperature and this indicated an increase in acoustic energy absorption as the material entered the superconducting phase.  The shear modulus and ultrasonic attenuation anomalies were explained using the second-order phase transition and short-range oxygen orderings in the Cu-O plane of the cell unit of this superconducting material.

Keywords: Acoustic properties; lattice vibration; microstructure; phase transition

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^*Corresponding author; email: ras@ukm.edu.my