What are the structural difference between oxides ( P4O6 and P4O10) of phosphorous?

According to “Bent Rule” loan pair prefer to stay to in those atomic orbital have more (S) character. And bond length is directly proportional to p-character. 

(1) In case of P₄O₆ molecules atomic orbital containing loan pair have more (s)-character and less (P) character hence shorter bond length while remaining orbitals have less (S) character and more (P) character hence longer bond length (X₁) than (X₂) in P₄O_{10 .}

(2) We know that On increasing % s character in hybrid orbital, the bond length decreases while bond angle increases.

(3) In Case of P₄O₆   (O-P-O) bond is Smaller due to higher P character in atomic orbital than orbital containing (O-P-O) in P₄O₁₀(have more s-character )

For reading more Details about  click on  Bent Rule andDrago's rule

Related Questions:

What is Bent’s rule of hybridization?

Which of the following compound have longest (S=O)bond length , O=SF2, O=SCl2, O=SBr2.

Why Bond length of O-O is greater in H2O2 than O2F2?

How to arrange increasing (C-H) bond length in increasing order and H-C-F bond angle in the given compounds, CH4, CH3F, CH2F2 and CHF3 ?