Nonstoichiometric oxide spinel system, Fe_(1.429)-_(x)Ni_(x)Al_(1.143)Si_(0.143)O_(4), has been synthesized via various heat treatments, and investigated by means of X-ray diffractometry, Mo¨ssbauer spectroscopy, and SQUID. The system shows three crystaltographic modifications. In the case of x = 0....
Nonstoichiometric oxide spinel system, Fe_(1.429)-_(x)Ni_(x)Al_(1.143)Si_(0.143)O_(4), has been synthesized via various heat treatments, and investigated by means of X-ray diffractometry, Mo¨ssbauer spectroscopy, and SQUID. The system shows three crystaltographic modifications. In the case of x = 0.0, the sample shows the coexistence of cubic spinel phase (a = 8.329Å) and α-Fe_(2)O_(3) (a = 5.3902Å, α = 53.2˚). When Fe ions are substituted by Ni ions, (0.043 ≤ x ≤ 0.1), the cubic structure of spinel phase changes to the tetragonal structure (a = 8.3229Å / c = 8.1027Å, a = 8.3098Å / c = 8.0563Å, a = 8.2987Å / c = 8.088Å) and α-Fe_(2)O_(3) to α-(Fe_(l-a)Al_(a))_(2)O_(3) (α = 5.394Å / a = 54.4˚ , a = 5.360Å / α = 52.4˚, a = 5.2911Å / α = 50.3˚ ). With increasing Ni content, a decrease of tetragonality is also observed. A mixed phase or a single phase spinel is possible according to the heat treatment in the range of 0. 143 ≤ x ≤ 0.429. Consequently, it has been confirmed that a single phase spinel including Si ions and cation vacancies can be formed for x ≥ 0.286 and a mixed one for x < 0.286 : the stable spinel phase is dominant with Ni content and sintering temperature. The analysis of Mo¨ssbauer spectra shollrs that Fe ions have only high spin state of +3 value with x ≥ 0.143 and Ni^(3+) ions occupy the tetrahedral sites. However, when the content of Ni ions is lower than 0.143, a coexistence of Fe^(2+) at the octahedral sites and Fe^(3+) at the tetrahedral- and octahedral sites is observed. From the analysis of the XRD pattern and Mo¨ssbauer spectra, an equation of cation distribution for the spinel phase could be established. The equation of cation distribution shows an Al/Fe ion mixing among tetrahedral and octahedral sites, though Al^(3+) ions have a strong preference for the octahedral sites, and a more stroger mixing of Al/Fe ions as the sintering temperature is lower. The observed Mo¨ssbauer line broadening at room temperature is interpreted as due to the distribution of the magnetic hyperfine fields caused by various cation distribution (x ≥ 0.143) and, partly, to the hopping process ( x < 0.143). The temperature dependence of the magnetic hyperfine fields and the low field magnetization, and the field dependence of the magnetization show that samples with x = 0.429 have a canted spin structure.
Nonstoichiometric oxide spinel system, Fe_(1.429)-_(x)Ni_(x)Al_(1.143)Si_(0.143)O_(4), has been synthesized via various heat treatments, and investigated by means of X-ray diffractometry, Mo¨ssbauer spectroscopy, and SQUID. The system shows three crystaltographic modifications. In the case of x = 0.0, the sample shows the coexistence of cubic spinel phase (a = 8.329Å) and α-Fe_(2)O_(3) (a = 5.3902Å, α = 53.2˚). When Fe ions are substituted by Ni ions, (0.043 ≤ x ≤ 0.1), the cubic structure of spinel phase changes to the tetragonal structure (a = 8.3229Å / c = 8.1027Å, a = 8.3098Å / c = 8.0563Å, a = 8.2987Å / c = 8.088Å) and α-Fe_(2)O_(3) to α-(Fe_(l-a)Al_(a))_(2)O_(3) (α = 5.394Å / a = 54.4˚ , a = 5.360Å / α = 52.4˚, a = 5.2911Å / α = 50.3˚ ). With increasing Ni content, a decrease of tetragonality is also observed. A mixed phase or a single phase spinel is possible according to the heat treatment in the range of 0. 143 ≤ x ≤ 0.429. Consequently, it has been confirmed that a single phase spinel including Si ions and cation vacancies can be formed for x ≥ 0.286 and a mixed one for x < 0.286 : the stable spinel phase is dominant with Ni content and sintering temperature. The analysis of Mo¨ssbauer spectra shollrs that Fe ions have only high spin state of +3 value with x ≥ 0.143 and Ni^(3+) ions occupy the tetrahedral sites. However, when the content of Ni ions is lower than 0.143, a coexistence of Fe^(2+) at the octahedral sites and Fe^(3+) at the tetrahedral- and octahedral sites is observed. From the analysis of the XRD pattern and Mo¨ssbauer spectra, an equation of cation distribution for the spinel phase could be established. The equation of cation distribution shows an Al/Fe ion mixing among tetrahedral and octahedral sites, though Al^(3+) ions have a strong preference for the octahedral sites, and a more stroger mixing of Al/Fe ions as the sintering temperature is lower. The observed Mo¨ssbauer line broadening at room temperature is interpreted as due to the distribution of the magnetic hyperfine fields caused by various cation distribution (x ≥ 0.143) and, partly, to the hopping process ( x < 0.143). The temperature dependence of the magnetic hyperfine fields and the low field magnetization, and the field dependence of the magnetization show that samples with x = 0.429 have a canted spin structure.
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#Nonstoichiometric Spinel 준강자성체 결정구조 산화물자성체
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