Existence of Deuterium peroxide Does deuterium peroxide exist? Wikipedia has no reference. Also, the sites for delivery of chemicals like "Pubchem" or "Chemspider" have no reference.

In my book, a preparation of $\ce{D2O2}$ is given,

$$\ce{K2S2O8 + 2D2O -&gt; 2KDSO4 +D2O2}$$

If $\ce{D2O2}$ exist, what are its physical properties (structure and appearance etc.)?
It does exist. At least Google shows one supplier situated in New Jersey.


  ID 1130   Deuterium Peroxide (30% in D2O) D2O2    98  5   5.0g / 10.0g


Though for some reason I could not find any reputable supplier like Cambridge Isotopes or Sigma-Aldrich (strange!). As far as physical properties are concerned, as pointed out by @snurden there exists a significant amount of literature. Here is one article from the Canadian Journal of Chemistry that includes study of many properties (behind a pay wall though).

Abstract:



And to answer final part of your question: