What structures nanoparticles and their eventual arrangements, which are not guaranteed to be crystals or close-packed structures, have, depends on their size, the structure of the particle "body" as well as their (ligand) saturation. There are hundreds of papers on tantalum nanoparticles already, I don't think there is a way around for you than to dig through a lot of them and see what publications match the particular NPs you want to study.

These are the crystal forms of bulk Ta2O5:

At least 2 polymorphs are known to exist. A low temperature form, known as L- or β-Ta2O5, and the high temperature form known as H- or α-Ta2O5. The transition between these two forms is slow and reversible; taking place between 1000 and 1360 °C, with a mixture of structures existing at intermediate temperatures.[5] The structures of both polymorphs consist of chains built from octahedral TaO6 and pentagonal bipyramidal TaO7 polyhedra sharing opposite vertices; which are further joined by edge-sharing.[6][7] The overall crystal system is orthorhombic in both cases, with the space group of β-Ta2O5 being identified as Pna2 by single crystal X-ray diffraction.[8] A high pressure form (Z-Ta2O5) has also been reported, in which the Ta atoms adopt a 7 coordinate geometry to give a monoclinic structure (space group C2).

Dear Bibek Thapa many thanks for asking this very interesting technical question. In this context, please have a look at the following potentially useful article which might help you in your analysis:

Prediction of New Ground State Crystal Structure of Ta2O5

https://arxiv.org/pdf/1711.07586.pdf

(see attached pdf file)

XRD characterization of tantalum oxide nanoparticles has also been reported in the following relevant reference:

Characterization and photocatalytic study of tantalum oxide nanoparticles prepared by the hydrolysis of tantalum oxo-ethoxide Ta8(μ3-O)2(μ-O)8(μ-OEt)6(OEt)14

Article Characterization and photocatalytic study of tantalum oxide ...

This paper is freely available as public full text on RG. A phase change of hexagonal to orthorhombic of Ta2O5 has been reported in the following article:

Solvent free synthesis of Ta2O5 nanoparticles and their photocatalytic properties

Article Solvent free synthesis of Ta 2 O 5 nanoparticles and their p...

One of the authors has an RG profile. Thus there is a good chance that you can request the full text directly from this author via RG (https://www.researchgate.net/profile/M-Seetha).

I hope this helps. Good luck with your research and best wishes, Frank Edelmann

P.S. One of the previous answers is a "good" example of copy-and paste-plagiarism from Wikipedia including even the reference numbers cited in the original text. Here is the original Wikipedia reference:

http://wikipedia.us.nina.az/wiki/Tantalum_oxide

Dear Bibek Thapa just in case that this is of interest to you: I just came across two interesting articles describing the use of tantalum oxide nanoparticles in drug delivery:

Drug-Loaded Mesoporous Tantalum Oxide Nanoparticles for Enhanced Synergetic Chemoradiotherapy with Reduced Systemic Toxicity

Article Drug-Loaded Mesoporous Tantalum Oxide Nanoparticles for Enha...

and

Tantalum oxide nanoparticles as an advanced platform for cancer diagnostics: a review and perspective

Article Tantalum oxide nanoparticles as an advanced platform for can...

Perhaps you can access these papers through your institution. Alternatively you can contact the authors directly via RG and request the full texts.

I don't think getting information from Wikipedia is a kind of plagiarism!

Dear Frank

I did some search about Ta2O5 in Google and found some good information about the structure of this oxide and I copied and paste it as an answer. Please tell me what's wrong with that?

I, perhaps should indicate the source of this information and your criticism is right.

Dear Mohammad Kooti thank you for your kind response. I think that in general there is nothing wrong with suggesting relevant information which is available on the internet. However, as you said, it is always advisable to cite the original source or reference. This will make your expert answer more helpful and valuable for other RG members.

With best wishes, Frank Edelmann

Dear Jürgen, Frank and Mohammad,

Thank you so much for your valuable answers.

While there are ample information for Ta2O5, I was seeking for TaO.

Thank you again.

Dear Bibek Thapa many thanks for your explanation. Of course, when chemists hear about "tantalum oxide" they immediately think of tantalum pentoxide Ta2O5. In contrast, tantalum monoxide (TaO) is a rather exotic material. In fact, I found a potentially useful article in which TaO has been synthesized in the form of "nanoneedles":

Electrochemical Synthesis of Nanomaterials in Molten Salts

Article Electrochemical Synthesis of Nanomaterials in Molten Salts: ...

Although this article has not been posted as public full text on RG, it is Open Access and can be freely downloaded as pdf file (see attached).

It is not clear to me if TaO is stable at ambient conditions.

Thank you so much Frank T. Edelmann The article is useful.