Sains Malaysiana 47(8)(2018): 1907–1911

http://dx.doi.org/10.17576/jsm-2018-4708-32

 

Superconductivity and Elastic Properties of La_1.85-1.5xSr_0.15+1.5xCu_1-xMn_xO₄

with x = 0, 0.02 and 0.04

(Kesuperkonduksian dan Sifat Kenyal La_1.85-1.5xSr_0.15+1.5xCu_1-xMn_xO₄ dengan x = 0, 0.02 dan 0.04)

 

NOR AZAH NIK-JAAFAR^1* & R. ABD-SHUKOR²

 

¹Pusat PERMATApintar® Negara, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia

 

²School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia

 

Diserahkan: 2 Februari 2018/Diterima: 27 Mac 2018

 

 

ABSTRACT

The effects of mixed-valence Mn substitution at the Cu site on the superconducting and elastic properties of La_1.85-1.5xSr_0.15+1.5xCu_1-xMn_xO₄ (x = 0, 0.02 and 0.04) were studied. The samples were characterized by X-ray diffraction (XRD) method, temperature-dependent resistance measurements, scanning electron microscopy (SEM) and sound velocity measurements at room temperature. An elastic softening and a decrease in the critical temperature Tc was observed as Mn was substituted for Cu. The Debye temperature θD for x = 0 and 0.02 void free samples were calculated to be 459 K and 430 K, respectively. Internal lattice strain which is related to lattice parameter ratio a/c did not correlate with Tc. The electron-phonon coupling estimated using the conventional Bardeen-Cooper-Schrieffer (BCS) theory was λ = 0.367 (x = 0) and 0.368 (x = 0.02). The electron-phonon coupling in two-dimensional van Hove scenario was calculated to be λvH = 0.0148 (x = 0) and 0.0149 (x = 0.02). These results were compared with other cuprates and related superconductors. The comparison showed that other than electron-phonon coupling, the elastic moduli might play an important role in the mechanism of superconductivity in these materials.

 

Keywords: Debye temperature; elastic moduli; electron-phonon coupling

 

ABSTRAK

Kesan penggantian Mn valens bercampur di tapak Cu terhadap sifat superkonduktor dan kenyal La_1.85-1.5xSr_0.15+1.5xCu_1-xMn_xO₄ (x = 0, 0.02 dan 0.04) telah dikaji. Pencirian telah dijalankan melalui kaedah pembelauan sinar-X, pengukuran rintangan elektrik melawan suhu, mikroskop elektron imbasan dan pengukuran halaju bunyi pada suhu bilik. Pelembutan sifat kenyal dan penurunan suhu genting Tc telah dicerap apabila Mn menggantikan Cu. Suhu Debye θD untuk sampel tanpa liang x = 0 dan 0.02 ialah masing-masing 459 K dan 430 K. Ketegangan dalaman kekisi yang berkait dengan nisbah parameter kekisi a/c tidak berkorelasi dengan Tc. Gandingan elektron-fonon telah dianggarkan menggunakan teori Bardeen-Cooper-Schrieffer (BCS) konvensional iaitu λ = 0.367 (x = 0) dan λ = 0.368 (x = 0.02). Gandingan elektron-fonon untuk senario van Hove dua dimensi ialah λvH = 0.0148 (x = 0) dan 0.0149 (x = 0.02). Keputusan ini telah dibandingkan dengan superkonduktor kuprat dan lain-lain superkonduktor yang berkaitan. Perbandingan ini menunjukkan bahawa selain daripada gandingan elektron-fonon, sifat kenyal mungkin memainkan peranan penting dalam mekanisme kesuperkonduksian bahan ini.

 

Kata kunci: Gandingan elektron-fonon; modulus kekenyalan; suhu Debye

 

 

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*Pengarang untuk surat-menyurat: email: norazah_nj@ukm.edu.my