Sains Malaysiana 38(2): 209-213(2009)

Electrical and Microstructural Properties of (La_1-xPr_x)_1/2Ba_1/2MnO₃ Compounds

(Kajian Elektrik dan Mikrostruktur dalam Sebatian-sebatian

 (La_1-xPr_x)_1/2Ba_1/2MnO₃)

Huda Abdullah

Faculty of Engineering, Universiti Kebangsaan Malaysia

43600 Bangi, Malaysia

S.A. Halim

Physics Department, Faculty of Sciences, Universiti Putra Malaysia

43400 UPM Serdang, Selangor, Malaysia  

Received:   26 April 2008 / Accepted:  14 July 2008

ABSTRACT

The electrical and microstructural properties of (La_1-xPr_x)_1/2Ba_1/2MnO₃ (x = 0.000, 0.167, 0.333, 0.500, 0.677, 0.833 and 1.000) compounds, prepared by the solid state reaction, have been investigated. The electrical property has been determined by using standard the four-point probe resistivity measurement with a temperature range of 30 K to 300 K. By increasing the Pr doping, the metal-insulator transition temperature (T_p) shifted to lower temperatures, which are 254, 248, 228, 220, 196, 180 and 158K for x = 0.000, 0.167, 0.333, 0.500, 0.677, 0.833 and 1.000, respectively. Using several theoretical models, it has been concluded that the metallic (ferromagnetic) part of the resistivity (ρ) (below T_P) fits well with the equation ρ = ρ₀ + ρ_2.5T^2.5, indicating that ρ₀ is due to the importance of grain and domain boundary effects, a second term ~ ρ_2.5T^2.5 appears that might be attributed to electron-electron scattering. The scanning electron microscope (SEM) micrographs show the grains size decreases as the level of porosity increases, which contributes to the increase resistivity.

Keywords: Metal-insulator transition; transition temperature;  resistivity

ABSTRAK

Sifat elektrik dan mikrostruktur bagi sebatian (La_1-xPr_x)_1/2Ba_1/2MnO₃ (x = 0.000, 0.167, 0.333, 0.500, 0.677, 0.833 and 1.000), yang disediakan dengan tindakbalas keadaan pepejal, telah dikaji. Pencirian elektrik ditentukan dengan menggunakan pengukuran kerintangan penduga empat titik piawai dalam lingkungan suhu daripada 30K hingga 300K. Dengan peningkatan Pr, suhu peralihan (T_p) beranjak ke suhu yang lebih rendah, iaitu 254, 248, 228, 220, 196, 180 dan 158K masing-masing untuk x = 0.000, 0.167, 0.333, 0.500, 0.677, 0.833 dan 1.000. Dengan menggunakan beberapa model  disimpulkan bahawa kerintangan (ρ) di kawasan logam (ferromagnet) di bawah T_p sesuai dipadankan dengan persamaan ρ = ρ₀ + ρ_2.5T^2.5.  Ini menunjukkan ρ₀ disebabkan oleh kesan penting butiran dan sempadan domain. Sebutan kedua ~ ρ_2.5T^2.5 berkemungkinan penyeraka elektron-elektron. Mikrograf  bagi mikroskop elektron imbasan (SEM) menunjukkan saiz butiran menurun dengan peningkatan keporosan, yang menyumbang kepada peningkatan kerintangan.

Kata kunci: Kerintangan; peralihan logam-penebat; suhu peralihan

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