Structural, optical and photoelectrochemical properties of p type Ni doped CuFeO2 by hydrothermal method

Doping‐Dependent Phase Fractions in Hydrothermally Synthesized Mn‐Doped CuFeO2

“…Additionally, in (3% and 6%) Ni-doped samples, a gradual decrease of the 2H fraction was published. [27] Thus, the peaked 2H phase fraction observed here for Mn doping complements and consolidates the previously mentioned studies. Based on the present data, the physicochemical reason for this behavior remains unclear.…”

“…The bandgap values for all samples are summarized in Table 1 and decrease up to an Mn content of x ¼ 0.1, beyond which E g,ind remains constant. Considering published experimental values ranging from 1.03 to 1.35 eV , [2,8,27] ab initio calculations yielding 1.3 eV for the rhombohedral R3 phase, [31] and the bandgap of the pure 2H phase of 1.33 eV, [20] the bandgap of undoped CuFeO 2 E g,ind ¼ 1.38ð1Þ eV, determined here, is reasonable. The same applies for the observed decrease of E g,ind with increasing Mn content x, which both corroborates the successful doping in line with the decrease of lattice Table 1.…”

“…parameters as well as unit cell volume and agrees with a similar decrease observed in the case of Ni doping. [27] Due to the proximity of the bandgaps of the R3 and 2H phases however, any further analysis with respect to the impact of Mn doping on the phase-specific bandgaps is effectively prevented. In contrast to its significant effect on phase fractions and the indirect bandgap, the Mn content had no observable effect on particle morphology.…”

“…This is much lower than Mn levels obtained in samples synthesized by solid-state reactions [13,21] but comparable to hydrothermal results for Ni-doped delafossite. [27] Moreover, rather strong discrepancies between nominal and actual doping levels were also found for Mg-and Ca-doped CuFeO 2 . [26,32] Two interesting questions result from these observations, which, however, cannot be comprehensively answered using the present data.…”

“…Moreover, a strong dependency of the 2H phase fraction on the Mn content is observed (see Figure 2) with the maximal phase fraction of about 27% for CuFe 0.99 Mn 0.01 O 2 . In general, the formation of both phases in doped and undoped samples is frequently observed following hydro‐ or solvothermal synthesis [ 19,25–27 ] under comparable basic conditions (2.2 mol L −1 NaOH in the presented case), whereas pure 2H formation requires very high basicity (more than 15 mol L −1 NaOH used by Jin and Chumanov [ 20 ] ). Investigations of Ca‐, Mg‐, and Ni‐doped and hydrothermally produced [ 19,26,27 ] are compatible with the presented results on 2H fractions though the latter studies were limited either to relatively low or high doping levels.…”