For an accurate measuremeent you need the intrupomental broadening. However, for 8 nm particlees you probably are looking a very wide peak, therefore if it is complicated to get the instrumental factor yes, you possibly can neglect it. The fitting: xrd peaks are best fitted to psudovoigt function, that contains lorentzian and gaussian contributions. But again, if your fittingg software

Yes, it is appropriate to use Gaussian, Lorentezian, pseudo-Voigt function etc.  to fit the peak profiles of the identified crystalline phases. With regarding to instrument influence in FWHM, it is well-known that instrumental broadening can change significantly the FHWM, and if you are intending to determine crystallite size, 1/FWHM*cos(angle), you should correct the FWHM using data taken on the same XRD diffractometer of a pure LaB6 powder standard or any other standard material. The crystallite size can be calculated based on the diffraction lines using Scherrer’s equation (disregarding microstrain and inhomogeneity). However, FWHM can be interpreted in terms of both lattice strain and crystalline size and, in general, the contribution of both effects to the width of a diffraction peak can be appropriately studied by the Williamson-Hall, which is quite realistic for separating strain broadening and size broadening in the presence of isotropic microstrain.

A. Leineweber, Parabolic microstrain-like line broadening induced by random twin faulting, Philosophical Magazine, 92:14, 1844-1864.

N.S. Gonçalves, J.A. Carvalho, Z.M. Lima, J.M. Sasaki, Size–strain study of NiO nanoparticles by X-ray powder diffraction line broadening, Mater. Lett., 72 (2012) 36-38.

https://www.researchgate.net/post/How_can_I_interpret_parabolic_Williamson-Hall_plot/1

Dear Dr. Das:

By hypothesis, whether the instrument error/ measurements errors are neglected, there is a serie of intrinsic sample contributions that can not be discarded or neglected. But, ina general way, the absence of instrumental contributions can not be hypothesized. It is necessary further correction.

It is possible that metal or metallic sample exhibits different type and concentration of defects from comparison with defects in oxides,  be "punctual" or "in line",  which exerts different types of contributions under the sample- diffractogram, at room temperature. In this way, seems interesting to implement a theory of analysis  that  a priori belong to the proper universe of the investigation.

Information about crystal symmetry, lattice parameter, crystallinity degree should be further considered to determine the best strategy to the approaching the question. See, there is a single information about the nanoparticle, its size is of the order of 10 nm. Depending on the unitary cell dimension of material, a large number of unitary cells exist in an sphere of 5 nm of radii. From this, a significative crystallinity degree can be expect and by consequence, a well behavioured diffractogram, in another words a complete set of diffraction lines can be observed. A least, this diffractogram differ of the diffractogram of material in its crystal form, by follow features typical of crystal: a high intensity for diffraction lines (cps at around 10000, see this number is ficticeous one only mentioned as a benchmark), diffraction lines well defined and constructed and the two-theta positions composes the proper reference.  In the diffractogram of the nanosized particles can be expect an intensity ten times below, diffraction lines are broad in its base and two-theta positions are all shifted to values higher than values reported to crystal. Here is mandatory the corrections if the work is about synthesis and characterization of the nanoparticle in question.There is the case where the particle is very small, also depending on the parameters above mentioned, in which due effects of scale, there is not the set of diffraction lines expected, instead there is only a "halo" a bump of small intensity and very diffuse diffraction line characteristic, sometimes an another and an another more.  In these cases, the full width at half maximum, assigned to a diffraction line that in general is correlated to event of order of 1/10 to some few degrees, has nota physical meaning. This "halo" has tens of degrees of width or close to this.

Thus, as commented in another contributions, it is necessary corrections and a good standard. Nowaday, it is not common such itens appears in the "corp" of the paper, stay implicity that  eventual correction was carried out. In a broad sense, further insigth about this can be reached in the classical book:

CULLITY, B. D. - Elements of X-ray diffraction, Third Ed.. New York: Addison-Wesley, 1967

The value of FHWD can be derived by theoretical adjust of diffraction line. I have used Gaussian function in the theoretical adjust of dielectric permittivity curves, infrared spectra etc., etc...The Gaussian function is symmetric with relation to curve center that is coincident with the maximum. If one or more diffraction lines are not symmetric does not possible a suitable adjust. In general, a Gaussian function is sactifastory up to the maximim, after maximum the adjust is unsactisfactory. Here is necessary some carefull since that there is assymetrical diffraction lines and set diffraction lines with some superimposition degree that gives a mimetic diffraction line with assymetric profile.  In this case, deconvolution of  "envelope" can be reached. But if there is not diffraction lines at very close two-Theta position and the base of diffraction line or lines is/are assymetrics is necessary to use another adjust functions as pseudo-Voigt, or another with further capability to cover the assymetric portion of diffraction line, typically the portion beyond the postion of two-theta maximum. There is a great number of them, the selection should be justified.

Kind regards

Marcos Nobre (MAL Nobre)

It is important to be always aware the material properties do not change with instrument or corrections. The material properties under defined conditions are fix. The measured data can be close to reality (material properties) more or less.

Thank you all

Of course instrumental peak broadening is a major issue in changing the FWHM values. Hence, a standard measurment should be done before using our samples

Thank you very much

is instrumental correction of fwhm in degrees or radians i was told only 0.1