i want to add a tab (page) after Deliveries & Invoices tab and add fields into my new tab

<record model="ir.ui.view" id="purchase_order_form"> 
<field name="name">purchase.order.form</field> 
<field name="model">purchase.order</field> 
<field name="inherit_id" ref="purchase.purchase_order_form"/> 
<field name="arch" type="xml">

<xpath expr="//page[@name='Deliveries & Invoices']" position="after">  
<page string='Terms & Conditions'> 
</page> 
</xpath> 
</field> 
</record>

i tried above code and update custom module it says 

Element '<xpath expr="//sheet/notebook/page[@name='Deliveries & Invoices']">' cannot be located in parent view